Develop Reference

dll and pdb are loaded, but "no symbols have been loaded for this document

I've looked through the answers to about 5 similar questions, and particularly the top page of answers to this 1.5k upvoted question, but none of the fixes in there do anything for me.
I've inherited a C# project and am trying to debug it. I'm a bit new at C#, but have more than a decade experience with Visual C++. So I know my way around the debugger a bit at least, and have had to deal with debugging DLL's before. However, this one has me stumped.
I can set breakpoints in the main project's .cs files and they work just fine, but when I try to set one in a sub-project dll ("assembly"?) all the breakpoints show up at runtime with "The breakpoint will not currently be hit. No symbols have been loaded for this document."
What I've tried:
Clean and rebuild.
Clean, delete all copies of the dll and pdb from my hard drive, rebuild.
Verified the project props are set to Define DEBUG constant, Define TRACE constant.
Set the subproject (assembly) as the startup project, with the main exe (in the same directory as the DLL and PDB) as the Start external program
In the project build settings, Debug Info is set to full, and Optimize code is not set.
The debug option Enable Just My Code is not checked (I checked it, there's no checkmark in the box).
I'm not trying to build or debug in a Release configuration.
I've also checked the loaded DLL in process explorer and the Symbol Load Information in the debugger, and they match:
Process Explorer:
VS 2012's Symbol Load Information:
So its clearly got some PDB loaded, its in the same directory as the DLL, and they both get built when I build the project. The timestamp on the two files is identical. Yet VS'debugger doesn't think symbols are loaded for that file.

Cannot find debugging information when debugging c++ dll

there:
The Application is build from C#, and the Dll is built from C++, and they are in different solution. When I Launch the Dll's debugger, there is always a message box pop up, which says "Debugging information for 'App.exe' cannot be found or does not match.Skipped loading symbols for NGen binary."
Thanks.
p.s. I've try putting the App.pdb in several location, but still don't work.

As commented by ortang, you need to activate the debug info when building your project.
See "/DEBUG (Generate Debug Info) (Visual Studio 2013)":
The /DEBUG option creates debugging information for the .exe file or DLL.
The linker puts the debugging information into a program database (PDB). It updates the PDB during subsequent builds of the program.
It is not possible to create an .exe or .dll that contains debug information.
Debug information is always placed in a .pdb file.
To set this linker option in the Visual Studio development environment
Open the project's Property Pages dialog box. For details, see Setting Visual C++ Project Properties.
Click the Linker folder.
Click the Debugging property page.
Modify the Generate Debug Info property.

First release with VS - a lot of output (not only an .exe), can I reduce?

after compiling a simple console application project for release I get a lot of output:
The .exe => thats fine, I need this for sure :)
MyApp.exe.config => Im using and changing this, thats fine
Some .dll files => these are the extern libraries Im using, I think thats fine too
Unknown:
MyApp.pdb
MyApp.vshost.exe
MyApp.vshost.exe.config
MyApp.vshost.exe.manifest
log4net.xml => huh, the config for log4net is already in MyApp.exe.config, why is another log4net config xml here?
Can I delete some of them without getting later trouble? Can I add the .dll´s somehow into the .exe (so that I dont have to copy always all the .dll with the .exe)?

This is expected, and all have purposes - but you are right: you don't need any of the "unknown" files, and can delete them (and certainly don't need to distribute them). For info:
MyApp.pdb is the debug symbols; useful for stacktrace, and for debugging later if problematic; you can disable this via the Debug Info option in the Advanced Build Settings dialog (Project Properties, Build, Advanced...) but I don't recommend it
MyApp.vshost.* is the debugger host process; you can disable this by disabling the "Enable the Visual Studio hosting process" option (Project Properties, Debug)
log4net.xml is the intellisense comments - useful for IDE usage when adding references

Those files aren't meant to be distributed to client pcs nor are useful for app to work properly: they're there (also) for debugging purpose.
If you want to "merge" dlls to your project, try using Microsoft utility ILMerge.

When you build your solution in release configuration there will be no *.vshost.*., this is an executable for debug hosting process.
log4net.xml you can remove, I believe.

You should be fine deleting/not deploying most of them.
If the dll's are managed assemblies you can use IlMerge which will add the dll's into the exe for you.

"Browse To Find Source" in Visual Studio 2010

When is "Browse To Find source" enabled in Visual Studio 2010? (see below)
In addition, I want to have it enabled so that I could browse to already-downloaded source code
files from http://referencesource.microsoft.com/.
This would be useful since Microsoft doesn't always release PDB/source code at the same time with their latest patches. So if I want to step for example into DateTime, I really don't care about the latest patches which didn't involve DateTime. I just want to browse to its code which I downloaded from http://referencesource.microsoft.com/.
After some investigations I found dia2dump which is a useful tool to view PDB file contents. (It's in C:\Program Files (x86)\Microsoft Visual Studio 10.0\DIA SDK\Samples\DIA2Dump\)
It looks like when I can't see source code for something like DateTime, using .NET Framework stepping, a mscorlib.pdb file actually gets downloaded.
But if you look inside it with dia2dump it doesn't contain source file mappings. In other words useless, because even if you could browse to the source code like my initial idea, it wouldn't work because there are no source file mappings and no start addresses of the functions, and a lot of stuff missing :(
I think the solutions here are to use .NET Reflector Pro for or keep a virtual machine at hand, with releases of the framework which have source code and then disable updates.

Introduction
Whenever you do a build from Visual Studio, normally, you also get a PDB file besides your executable file. You can see this file in the ..bin\Debug or ..bin\Release directory.
This PDB file keeps a mapping to your source code lines and executable code in your assembly. Also, the original locations of the source code files from which a build was done is stored inside a PDB file.
This means that if you build a class library which had a single file located at G:\ClassLibrary\Class1.cs, this path will be stored inside ClassLibrary.pdb.
What is important to remember from all this is that without a PDB file it is impossible to do source code step-in debugging.
Real-life scenario
So, suppose I do a build on my drive G:\ClassLibrary1, for a class library.
I give you a ClassLibrary.dll and a ClassLibrary.pdb file, or you get them by checking them out from source control.
You reference the ClassLibrary.dll in your project and you use a class from the library.
If you now try to step into class code from the library the following will happen:
Visual Studio tries to locate a ClassLibrary.pdb file in a couple of locations
1.1 If it doesn't find it, you get a "Browse to find source" disabled
page. Remember, you can't debug without a valid PDB file.
1.2 If it does find a PDB file, it looks inside the PDB file and sees that you are trying to debug Class1.cs which was originally built from
G:\ClassLibrary1\Class1.cs
and looks on your computer for that file.
1.2.1 If it finds it, it steps into the code automatically.
1.2.2 If it doesn't find it, you get the following dialog:
If you press Cancel, you will be presented with the: "No source available" and you will have "Browse to find source" enabled in this case.
Why? Because you have a valid PDB file, but Visual Studio can't possibly know where you have the source code for ClassLibrary1 on your computer or if you even have it on your computer. That's why you got the dialog -> so that you can point Visual Studio to the exact location of the source code file.
Final notes
So what will you do when you get a browse to find source disabled?
In Visual Studio, you open menu Debug -> Windows -> Call stack.
You right click on the top call stak instruction and you choose "Symbol Load Information". It will show you the locations where Visual Studio has tried to find a valid PDB file.
1.a If you only see "Cannot find or open PDB file" messages put a valid PDB file at any of these locations. (You might have to scroll right to see the messages) Stop and start debugging again.
1.b If you see a "PDB does not match the image" message it means the following. Visual Studio has found a PDB file, but it is for another build. If I build ClassLibrary1.dll and give it to you, and then I build it again without changing a single line of code and then give you the PDB, and you try
to debug classLibrary1.dll you will get this message. The assembly and its PDB file must be exactly from the same build, otherwise you will get this message. (This check is done using some unique number put inside the assembly and PDB file every time you do a built)
1.c You see a "symbols loaded" message but still get a "Browse to find" disabled. It means that the PDB file you have is not good for step-in debugging. Some PDB files you try to use don't have all the information in them necessary for step-in debugging. I think you can control this from somewhere in the advanced build settings, but I haven't tried it though, because I want to have usable PDB files generated everytime I do a build. This situation often happens if you try to debug the source code of the .NET framework itself and Microsoft hasn't put usable PDB files for the source code, but instead Microsoft has put some PDB files which can't be used for step-in debug. This happens more often than you think, because often Microsoft makes updates (patches) to the .NET Framework source code. These updates silently install onto your computer via Windows Update, and you are surprised to see that yesterday you could debug .NET Framework source code and today you can't. It usually takes some time until they put a valid PDB file for the latest code. In this case you can use .NET Reflector Pro step-debug ability or a virtual machine which has a .NET framework version with usable PDB files and disable Windows Update on that machine.

Check out the article Step Into .NET Framework 4.0 Source Code.
If you encounter the “No Source Available” screen, try to press “Browse to Find Source” and find the file you need in the source directory. You should probably need to use files search to find it.
This is done only once, since from now on Visual Studio remembers this location and searches there for missing source files.
I hope it's about what you are looking for.

Similar issue in Visual Studio 2019 can be resolved by checking "Enable Just My Code".
Debug > Options... > Debugging > General > Enable Just My Code
More detail explanation can be found here How to fix debugger is looking for executioncontext.cs

a matching symbol file was not found in this folder

I want to use debug symbols, but I am receiving the following error:
a matching symbol file was not found in this folder
What is this problem, and how to solve it?

One of the things I've ran into with was because debug was off on the project referenced where the code lives. In my case, I made a new configuration called "Developer" and by default debug was turned off.
Right click the project in question
Properties
Build
Advanced (right bottom corner)
Set Debug Info to full
Recompile

I had the same problem as #DmainEvent. Apparently the dll that I was using was not the same version as the pdb that I had just compiled, so I got the error message.
If you have this problem, try using the dll and pdb from the same compilation run.

The error I got was "a matching symbol file was not found in this folder" in the Debug => Modules window even after both the DLL and PDB were available and built together, so I was unable to debug into the target DLL referenced by my main project.
Posting this here in case it helps someone browsing with "Mixed Platform" build for target DLL. I did two things to get past this:
In the solution using the target DLL, Uncheck "Just My Code" in Tools => Options => Debugging => General => Enable Just My Code (JMC).
Check "Enable native code debugging" in target DLL solution in relevant Project Properties => Debug.

I tried all the possible solutions, finally it worked when I disabled the option Enable native code debugging under the Debugger engines of Properties > Debug.

I ran into this problem and the answer was simple.
Visual studio has two project level settings that can create .pdb files.
Linker: Configuration Properties -> Linker -> Debugging -> Generate
Program Database File = "xxxx.pdb"
Compiler: Configuration Properties -> C/C++ -> Output Files -> Program Database File Name =
"yyyy.pdb"
You want #1 for debugging. Forget about #2.
Give file #2 a different name than file #1 to solve this error.
I don't know why microsoft specifies #2 as a .pdb file. That is just confusing.

I have fixed my debug symbols, forcing them to match using this tool:
chkmatch tool
edit: the website is down now. the wayback machine helps: https://web.archive.org/web/20210205095232/https://www.debuginfo.com/tools/chkmatch.html
So, my problem was I was trying to debug my project and the debugger couldn't step-in to the in-house nugets sources. I had the source files of the nuget project. Still the visual studio didn't accept the pdb files I was trying to show it to.
Showing exact same error:
a matching symbol file was not found in this folder
So, what I did was I added this to the .proj file of the nugets project:
<DebugType>full</DebugType>
And created the dll and pdb file again using the rebuild option.
In the command line I ran:
.\ChkMatch.exe -m name_of_your.dll name_of_your.pdb
It said this:
Writing to the debug information file...
Result: Success.
Great success!
So, next, I referenced this dll instead to the proj I was trying to debug. I worked when I tried to load the symbol again.
Hope it helps.

Without more details as to what you're doing, it's difficult to go beyond "the debugger is looking for a symbol file which matches the compiled code, and couldn't find one in the folder where the compiled code lives."
Some things to think about:
Are you creating symbols as part of your compilation? (check the project properties)
Are you using a symbol server (if so, does it point to the right place)
Is this compiled code from a third party? In which case, as you apparently have the source, compile it yourself.
Consider clarifying your question if you want a better answer. Especially what do you mean by "I want use of Symbols".

For BizTalk (and other) projects, it could be because there's a version of the assembly you're trying to debug already in the GAC. When you run a unit test or hit F5 to debug, a new version is compiled locally. However, the version in the GAC is being used, and the newly created PDB doesn't match the DLL in the GAC.
One way around this is to deselect a build for everything except your unit test project using the Configuration Manager, as shown below:

Well, the solution depends on your specific problem. I tried everything that could be possibly found on Stackoverflow and other sites. One of the thread that I followed is this. That did not help too.
The problem was at once resolved when I noticed that my executable project did not contain a reference to the library that I wanted to debug. So I just added the reference to that project.
**PS: ** This problem might also arise because the assembly referenced by the executable assembly might not match that in the references. So in that case, you just remove the already existing reference and add the new one.
Hope this helps!

The same happen to me because the .pdb file of the project have not been copied to the debug\Bin folder, so the symbols could not be loaded from the .pdb file.
You must rebuild your project and manually copy the symbols (.pdb file) to the debug\Bin folder of executable project.

I was trying to load symbols for a installed nuget package published on our local dev server. I had to uninstall and add a normal reference built from the code instead. This worked for me. Just remember install the original nuget package again once finished debugging.

If it works for you, try to embed debug symbols in the dll itself, so the symbols are loaded automatically. This worked for me in netcoreapp3.1 and net5.0:
<DebugType>Embedded</DebugType>
<EmbedAllSources>True</EmbedAllSources>
Beware that you may find this in documentation:
<AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>
but it does not work.

I ran into this with Visual Studio 2022, tried the most of answers here. Fixed by switching back to Visual Studio 2019, seems like a bug in 2022.

My issue was a bit simpler to resolve, but still the issue the question asked. At first, I was not publishing the pdb file with the nuget package another project was using. Once I confirmed that, I removed the nuget package from my project and readded it from our network nuget source. That still didn't let Visual Studio pick identify the PDB location.
Then I noticed that if you select one of your nuget packages, ( Project --> Dependencies --> Packages --> Choose nuget package), there is a Path property. I checked that location and it pointed to %USERPROFILE%.nuget\packages. The pdb was not at this location and the Date Modified was older than the latest package I published. Once I deleted the folder for the given package version, removed it from my project, and re-added it, the latest .dll and .pdb file were added to this location.
After that, I was able to step into the code of my nuget package and had no further issues.
To get the nuget project to produce the pdb file in the first place, I added <IncludeSymbols>true</IncludeSymbols> inside of a PropertyGroup within the csproj file as other answers had directed.
Once I rebuilt that nuget project, it generated 2 *.nupkg files:
Namespace.x.x.x.x.nupkg
Namespace.x.x.x.x.symbols.nupkg

I found this was because the Properties => Debug => Start Action was set to Start external program instead of the Project. So the newly generated pdb file didn't match, because the actual exe was the wrong one.

I have had this problem recently as well.
Was able to fix it by selecting MyProject->Properties->Linker->Debugging->Generate Debug Info->"Optimize for debugging (/DEBUG)".