What happens if you convert the PDF to DOCX with calibre's default settings?
What happens if you open the PDF in Word? To do that you'll need Word 2016, or maybe Word 2013, I skipped that one.
And, have you read the following stickies at the top of the Calibre->Conversion sub-forum ==>>
Read this before Posting PDF Questions and
How to ask a question about conversion problems
BR