msdxm.tlb

COM type library Reference

A .tlb file is a type library for the Component Object Model on Windows. The binary file describes the interfaces, methods, and types of a COM component. Development tools read the library and generate the code that calls the component. Script engines use it for late binding. Many system components ship a .tlb file next to their DLL.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.