While Export the PDF file, Optical Character Recognition engine runs on the PDF files & recognizes the text before exporting it to other file format. So it completely depends on the quality & structure of the PDF file. If the file is created in Acrobat then you will get the best result while Exporting it to other file formats.
However try using the Export PDF service online https://cloud.acrobat.com/exportpdf , check if you see any difference.
I see the missing words from the last export I did, although it still has the extra page breaks. I don't know how the document was created as I didn't create it originally. Just wishing I could be confident that the Word doc I send back to my client hasn't been altered except for the page breaks this time. He made his edits last time, I re-formatted, and then he discovered all sorts of things out of place.
You might how the document and possibly the source format by inspecting the prop terries of the PDF.