First import the PDF into Calibre. With Calibre you can converse the PDF to other formats, e.g. to WORD. And the text in WORD can be imported into LINGQ.
Pdf is difficult to convert import E-book conversion — calibre 6.21.0 documentation If you are getting error messages on the ctrl v probably best to try Calbre conversion. At least you are woking with a Latin left to right language. In Hebrew and Arabic I’ve encountered everything from throwing sentences out of order to having individual words spelt backwards to just gibberish code.