If it wasn't saved as a tagged PDF (which the vast majority of PDFs out there aren't), you'll have a tough time editing or even converting it, regardless of the software used. And it probably won't look right either, with differences in line or paragraph width, differences in fonts, etc.
It's a lot better to go back to the original document from which the PDF was created, edit it, then save (export) it as a PDF. If you don't have the original document, OCR-ing it and doing the grunt work that I mentioned earlier is your next "best" thing.
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