PDF to Word: what really happens to your document
A PDF is a picture of a layout, not a document
Adobe created PDF in 1993 so a page would look identical on every screen and printer, and it became an open ISO standard in 2008. To achieve that, a PDF stores text at fixed positions. A Word file stores paragraphs, styles and tables. Converting means guessing the second from the first.
Why Word-made PDFs convert better
A PDF exported from Word still carries clues about headings, lists and tables, so the guess is usually close. PDFs exported from design software, or printed from a web page, contain far fewer clues and need more cleanup.
Tables and columns
Genuine tables survive best. Multi-column articles and forms with boxes are harder, because the reading order has to be inferred. If text lands in the wrong order, check the columns first.
A quick checklist after converting
Scroll to the last page, since shifted page breaks show up there first. Look at every table, check that images sit beside the right text, and run spell check, which also catches the odd misread character.
When not to convert
If you only need to change a date or a name, ask the sender for the original file. A converted document is a good draft, but the original is always the better source.
If the file is a scan, extract the text with OCR and paste it into Word. Converting a scan directly gives you pictures, not words.