I'm pretty sure this is a bug with iOS, not Adobe. All my PDFs generated from iOS are called "PDF文档" as well. My language has always been set to English. This is a fairly recent bug, I haven't noticed this before iOS 13.
You can easily replicate this bug using only native Apple software, no third party software needed.
Take a screenshot of any site in iOS Safari
Tap the screenshot, then tap 'Full Page' (for PDF)
Save the PDF to Files
The PDF will show up as "PDF文档".
It seems iOS is adding random Chinese looking characters for no apparent reason.
(I do have Adobe software installed, but it seems unlikely Adobe apps would be able to effect Safari/Files apps default behaviour)
I hope Apple addresses this in an upcoming iOS update.