On windows Ctrl-c tab to browser Ctrl-v will paste the clipboard into an untitled import tiddler.
Try rclick to copy to see if the source provides alternate copy formats. Change the source or viewer if not.
If you use the visual editor you can have this stored as html in a tiddler.
If you collecting content look into browser extensions, yes they display pdf or advance clipboard tools.
Tiddlyclip works well but only for the browser but pdf can be in the browser.
I use snagit to capture content and grab text from images. I use foxit reader for pdf handling.
See how you go and ask more questions here.
Regards
Tony