Process Explorer shows you information about which handles and DLLs processes have opened or loaded.
The Process Explorer display consists of two sub-windows. The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you’ll see the handles that the process selected in the top window has opened; if Process Explorer is in DLL mode you’ll see the DLLs and memory-mapped files that the process has loaded. Process Explorer also has a powerful search capability that will quickly show you which processes have particular handles opened or DLLs loaded.
The unique capabilities of Process Explorer make it useful for tracking down DLL-version problems or handle leaks, and provide insight into the way Windows and applications work: https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer.
How to use it is also described, e.g., under
https://www.techsupportalert.com/content/how-find-out-which-windows-process-using-file.htm or
https://helpcenter.gsx.com/hc/en-us/articles/115015880627-How-to-Identify-which-Windows-Process-is-Locking-a-File-or-Folder.