If all one wants to do is fix a couple of things, then PDF conversion to epub is NOT for you. It will take an entire day at best, a week or more at worst.
You can try Mobipocket Creator with WINE to get an html file loadable into Sigil and see what you get. But one or two errors from PDF to epub, exceedingly unlikely. Almost anything requiring fixed formatting will fail in epubs.
If your pdf viewer has a text mode, you use it on the pdf in question to see if any text is part of the pdf, and what shape it is in. Much text mode conversion that is added to pdfs is only to make it searchable and they don't tend to worry too much about accurate text.
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