[Quoth]

Originally Posted by PetBest

Libreoffice can read PDF and convert it to .odt format (and also to .docx format ).
Both formats .odt and docx can be imported by Calibre.
See here: https://itstillworks.com/convert-pdf...u-8419833.html

Not really, Not MS Word either. And only SOME PDFs at all.
PDF is a rubbish source for conversions. It's an envelope with any mix of text, postscript, vector images, bit maps and layers.
PDF is only intended to be viewed as is or printed. It has a defined page size. Real ebooks have no page size at all and reflow/repaginate according to window (desktop) or screen.

The only 100% assured method of PDF conversion is to convert to images, OCR, proof the OCR text, format in WP and save docx, then make an ebook.

Sometimes you can extract original text or an OCR layer. It's so much bother that unless it's for legal commercial production of ebooks that it's simpler to have a big enough screen to read the PDF as designed.

Also if you use LO Writer at all:
1) Only edit ODT, even if you import docx or rtf or HTML
2) Save As docx an extra copy for Calibre.

Only import docx, not odt or RTF or HTML or text etc if making an ebook. Make epub first and convert that for other formats.

Of course you can import any ebook format (except PDF) and convert in Calibre, but if source is really stupid you might want to export docx or even RTF and fix headings, styles etc in Word or LO Writer.