I understand that you're looking to convert an uploaded (attached) PDF file into a Jive native document. Unfortunately, the content resides in Jive as an attachment and there isn't an out of box mechanism to convert this. You might try manually extracting and copying the content over using a PDF viewer or editor app, but you'll likely run into formatting issues.
If this is something you'd like to see in future versions, I'd recommend submitting a feature request idea in the Ideas for Jive space to help capture this for our Products Team.
I hope this helps answer your question. Let me know if you had any other questions on this.