Receiving a PDF attachment from a sender using Outlook has a weird extension and I cannot open the File

Greetings,

I have a PDF. It is NOT open in another program.

If I send it as an attachment using Microsoft Outlook (latest in Office 365), it seems to add an underscore after the "." in the extension.

This only seems to happen with filenames longer than 72 characters.

IE:  72charactorfilename.pdf becomes 72charactorfilename_._pdf