A desktop publishing application from Microsoft that focuses on page layout and graphic design.
If you still have Publisher installed, Microsoft’s PowerShell sample (and the community macros on this thread) is still the free path for thousands of files. That sample fails a lot for ordinary reasons: you are not in the script folder, execution policy blocks it, or Publisher / Office interop is missing.
If Publisher is gone from your machines, or PowerShell is not realistic for your team, there is another option. Full disclosure: I built PubConvert for Windows.
It is a paid Windows app on the Microsoft Store. It converts .pub files on your PC without needing Publisher installed, including large batches (thousands of files):
apps.microsoft.com/store/detail
I am not affiliated with Microsoft. This is a third-party app I made. Happy to answer practical questions if anyone tries it.