Recents folder not showing pdf files

I am using MS Office 365 on a Macbook Pro with OS X

I use Word and Excel and save documents in separate folders on OneDrive.

I then want to access these documents ie. attach them to a outlook email message. When I go to the Recents folder in Finder the .docx or .xls files are there but not the PDf files. I then need to navigate to the separate folders to see and choose the pdf files.

Is this a bug on my side that can be fixed?

tx

Stephen