You convert a PDF, open it in Word, and it looks perfect. Then you try to change a sentence, and the document falls apart: the text will not reflow, the cursor lands somewhere unexpected, and deleting a line leaves a hole where it was.
What you have is a page with a box drawn on it for every line of the original. Each box holds one line, pinned to the coordinate it occupied in the PDF. It is a picture of a document assembled out of movable parts, and it is the single most common complaint about PDF-to-Word conversion.
Why it happens
Because a PDF does not contain paragraphs, and reproducing its appearance is far easier than working out what it means.
A PDF is a list of drawing instructions: put these characters at 214, 588 in 11pt Times. There is no paragraph, no heading, no list, and no reading order. Those things exist in your eye, not in the file.
So a converter has two options. It can place each fragment in a box at the same position, pixel-perfect, zero interpretation, completely inert. Or it can try to infer the structure: which lines belong to one paragraph, which are headings, what order any of it should be read in.
The first is easy, always looks right, and lets you claim your converter "preserves formatting perfectly". The second is inference, it can be wrong, and it produces a document that no longer matches the original exactly. Most converters take the first.
The trade nobody states plainly
Here is the thing the marketing never says: you cannot have an exact visual match and an editable document. They are opposite properties.
An exact match means every piece of text stays at a fixed coordinate. Editable means text moves when you type. A file cannot do both. So when a converter promises "perfect formatting and full editability", it is delivering the first and describing the second.
Knowing which you want makes the choice easy. If you want the layout, keep the PDF, it already is the layout. If you want to edit the words, accept that the layout will change, and pick a converter that produces real paragraphs.
What a good conversion has to do instead
Find the reading order. On a two-column page the columns share their baselines, so reading across the page interleaves them. The columns have to be detected from the geometry before any text is emitted.
Rejoin the paragraphs. This is the one that decides whether the file is usable. A PDF breaks a line wherever the column ran out; those breaks are meaningless. Preserve them and every line becomes its own paragraph, which is why so many converted documents will not reflow even when they are not made of text boxes.
The hard part is keeping the breaks that do mean something: between genuine paragraphs, and around list items. A hyphen at the end of a line usually means a word was split and should be rejoined; a line starting with a bullet should never be merged into the sentence above it.
Detect the headings. Font size relative to the body text is the main signal, but size alone misfires, the first line of a paragraph in a slightly larger face becomes a heading. Requiring that a heading also be short and not end in a full stop makes it far steadier.
How to tell what you have been given
Open the converted file and click into the middle of a paragraph. Now press End.
If the cursor goes to the end of the visual line, you have text boxes or one-paragraph-per-line. If it goes to the end of the whole paragraph, possibly several lines down, you have a real document.
The other quick check: turn on formatting marks (Ctrl+Shift+8). A paragraph mark at the end of every visual line means the paragraphs were never reassembled.
What to do about it
If you already have a bad conversion, the clean-up guide covers the fastest route to a usable document, and for a text-box file, honestly, reconverting is usually quicker than repairing.
The converter here does the three inferences above and tells you how many lines it joined, so you can see whether the work was done rather than assuming it. It runs in your browser, so the document is not uploaded anywhere.