The HDMP file extension stands for Heap Dump file. HDMP files store system data recorded when an error occurs. They are binary files saved to disk. HDMP files provide no benefit if opened without the right applications.
HDMP files are uncompressed memory dump files. In contrast, MDMP files are compressed mini dump files. Compression reduces file size for sending to Microsoft to report issues.
If Microsoft Visual Studio is installed but .HDMP files do not open, ensure the software is up-to-date. Sometimes newer versions of applications introduce new formats. This can prevent older versions from opening newer file types like .HDMP.
You typically should not open .HDMP files unless diagnosing a program crash in a controlled environment. Over 400 file formats can be opened with File Viewer Plus software. Microsoft Visual Studio for Windows, Notepad++ and more can open .HDMP files.
Windows Debugger
Visual Studio
WinDbg