I do know that entering text strings in the "Description" in the Project Panel for a file imported into PPRO will change metadata for the file IN the PPRO project. These descriptions will stay in the project, for any file.
If you want to try and get the description text strings to migrate to other programs that read XMP metadata, you'll need to go to the Metadata panel (nested with the Source Monitor) and activate the "Link" icon under "Clip" tab for "Description" and then make sure this same "Link" icon is activated in the "File" XMP area under "Dublin Core" "Description".
You'll then see your text strings populating into the XMP metadata, from the project. Then next thing is to make sure the other program you want to see the text strings can read XMP metdata. If the program can't read XMP metadata, then you'll not see the descrptions you entere for the files in PPRO.
I hope this helps!