reading an application's manifest file?

Windows manifest files are Win32 resources. In other words, they're embedded towards the end of the EXE or DLL. You can use LoadLibraryEx, FindResource, LoadResource and LockResource to load the embedded resource.

Here's a simple example that extracts its own manifest...

BOOL CALLBACK EnumResourceNameCallback(HMODULE hModule, LPCTSTR lpType,
    LPWSTR lpName, LONG_PTR lParam)
{
    HRSRC hResInfo = FindResource(hModule, lpName, lpType);
    DWORD cbResource = SizeofResource(hModule, hResInfo);

    HGLOBAL hResData = LoadResource(hModule, hResInfo);
    const BYTE *pResource = (const BYTE *)LockResource(hResData);

    TCHAR filename[MAX_PATH];
    if (IS_INTRESOURCE(lpName))
        _stprintf_s(filename, _T("#%d.manifest"), lpName);
    else
        _stprintf_s(filename, _T("%s.manifest"), lpName);

    FILE *f = _tfopen(filename, _T("wb"));
    fwrite(pResource, cbResource, 1, f);
    fclose(f);

    UnlockResource(hResData);
    FreeResource(hResData);

    return TRUE;   // Keep going
}

int _tmain(int argc, _TCHAR* argv[])
{
    const TCHAR *pszFileName = argv[0];

    HMODULE hModule = LoadLibraryEx(pszFileName, NULL, LOAD_LIBRARY_AS_DATAFILE);
    EnumResourceNames(hModule, RT_MANIFEST, EnumResourceNameCallback, NULL);
    FreeLibrary(hModule);
    return 0;
}

Alternatively, you can use MT.EXE from the Windows SDK:

>mt -inputresource:dll_with_manifest.dll;#1 -out:extracted.manifest

You can extract/replace/merge/validate manifests using the command line manifest tool, mt.exe, which is part of the Windows SDK:

C:\Program Files\Microsoft SDKs\Windows\v6.1>mt /?
Microsoft (R) Manifest Tool version 5.2.3790.2075
...
> To extract manifest out of a dll:
mt.exe -inputresource:dll_with_manifest.dll;#1 -out:extracted.manifest

Different locations:

• C:\Program Files\Microsoft SDKs\Windows\v6.1\bin
• C:\Program Files (x86)\Windows Kits\10\bin\10.0.18362.0\x86

There's a manifest viewer tool available here -- I don't know if the author will make source code available.

The easiest way to view/edit manifests in compiled apps is using Resource Tuner: http://www.restuner.com/tour-manifest.htm

In some cases, it's more robust than mt.exe from MS, and it's a visual tool.

As a side reminder: remember that manifests can also be standalone files with the same name as the app (extended by ".manifest").

So if you want to check out which manifest is really used at runtime, this must be taken into account.

Sysinterals "sigcheck -m" dumps the manifest of an exe. (You can wget from live.sysinternals.com).

Sigcheck - Windows Sysinternals _ Microsoft Docs