Why a Word document can change when it is converted to PDF

A .docx is a description, not a page

A PDF records finished pages: this character, in this font, at this position. A Word document records something looser — paragraphs, styles, a page size, margins — and leaves the layout to whatever opens it. Line breaks, page breaks and where a table splits are calculated every time the file is opened, by that application, with the fonts installed on that machine.

When you use Save as PDF inside Word, that calculation is Word's, with your fonts, and the PDF records exactly what you saw on screen. When a converter on a server does it — this site's Word to PDF, or any other online converter — the document is laid out a second time, by different software, on a machine with a different set of fonts. Most of the time the two results are the same. When they are not, fonts are almost always the reason.

Which fonts come through unchanged

We measured it on our own conversion engine, setting the same paragraph in six common fonts:

• Calibri, Cambria, Arial and Times New Roman are drawn in Carlito, Caladea, Liberation Sans and Liberation Serif. Those are metric-compatible: every character has exactly the same width as in the original, so every line breaks in the same place and every page ends on the same word. The letters look very slightly different; the layout does not change.
• Aptos and Segoe UI have no such twin, and were drawn in DejaVu Sans, a different font with different widths. Lines break in different places, a paragraph can gain or lose a line, and a page that was full can spill onto the next.

Aptos matters more than it sounds: it has been the default font in Microsoft 365 since 2023, so a document typed recently with no font chosen is set in it.

Three ways round it, in order of how reliable they are:

• If you have Word, export from Word. File, then Save As, then PDF. The layout is then Word's own, and nothing is recalculated.
• Use one of the four fonts above for documents that will be converted elsewhere. Their substitutes keep the layout identical.
• Embed the fonts in the document. In Word: File, Options, Save, then Embed fonts in the file. A converter that reads embedded fonts then uses yours. Word only embeds fonts whose licence allows it.

This is a different problem from a PDF that looks wrong on someone else's computer, which happens when a PDF was made without embedding its fonts — why a PDF looks different on another computer covers that one.

Tracked changes come with it

This is the one to check every time, because it can put something in front of a reader that you believed was gone.

A Word document with tracked changes still contains every deletion until the changes are accepted. We tested it: a price line edited from 9,000 to 12,000 with tracking on converted to a PDF that shows both numbers: the old one struck through, the new one underlined, with a change bar in the margin. Anybody you send that PDF to can read the figure you deleted.

Before converting, open the Review tab and choose Accept All Changes, then convert. Comments, by contrast, are left out of the PDF — but they stay in the .docx, so delete them before you send the Word file itself to anyone. Afterwards, PDF to text is a quick way to confirm nothing you deleted is still in the file — it shows every word on every page, including any that are struck through.

The smaller differences

Beyond fonts, a second layout engine occasionally disagrees with Word about details:

• Tables set to fit their contents can choose slightly different column widths, which moves a row onto the next page.
• Text wrapped around a picture can wrap a line earlier or later.
• A table of contents is printed as it was last updated in Word. If you added a section afterwards, update the table in Word before converting (right-click it, then Update Field) — the converter prints it as it was saved.
• SmartArt and some chart styles are drawn from the picture Word stored with them, which is usually exact and occasionally a simplified version.

None of these is common, and all of them show up in the same check.

A two-minute check on the result

Open the original and the PDF side by side and look at three things.

• The page count. If the PDF has one more page than Word showed, a paragraph re-wrapped somewhere. PDF page count gives you the number without opening anything.
• The last line of each page. Re-wrapping shows up there first: a page that ended on a sentence in Word ends mid-sentence in the PDF.
• Anything that must not move — a signature block, a figure caption, a total at the bottom of a page.

If you have an earlier PDF of the same document, Compare PDF finds every difference between the two. How to check a converted document covers the checks that matter for figures and tables, and converting Word, Excel and PowerPoint to PDF covers what each format loses on the way.