PDF vs DOCX — which format should you send?

People treat PDF and DOCX as interchangeable ways of storing a document. They aren’t. They’re built on opposite assumptions, and picking the wrong one is behind most “it looked fine on my computer” disasters.

The core difference

DOCX describes content. It says: this is a Heading 1, this is a paragraph, this is a table with three columns, use Calibri at 11pt. How that becomes pages is decided when the file is opened — by which app, which version, which fonts are installed, and what paper size is set.

PDF describes appearance. It says: draw this glyph at this coordinate in this font at this size. Pages are already decided. Everyone sees the same thing.

Everything else follows from this.

Why a Word file looks different on someone else’s machine

Because it’s re-laid-out on arrival.

If the recipient lacks your font, Word substitutes one. Substituted fonts have different letter widths, so line breaks move, and everything after them shifts. Add a different Word version, a different default paper size, or Google Docs’ rendering engine, and a two-page CV becomes three, a table splits across pages, and your cover image ends up alone on page one.

None of this is a bug. It’s the format working as designed — DOCX is meant to reflow, which is exactly what you want while you’re writing.

Send a PDF when

• Anyone is judging the presentation. CVs, applications, proposals, portfolios.
• It will be printed. PDF is the only format that reliably prints identically.
• It’s a record. Invoices, contracts, receipts, certificates — anything where “what did it say” might matter later.
• You don’t know what software they have. PDF readers are near-ubiquitous; .docx support is patchier.
• You don’t want casual edits. Not security, but it does stop accidental changes.

Send a DOCX when

• They need to edit it. Sending a PDF to someone who must revise it just creates work.
• It’s going through review cycles. Track changes and comments are DOCX features.
• They’ll reuse parts of it. Templates, boilerplate, briefs.
• It’s a form to fill in. Unless it’s a proper PDF form with fields.
• It must stay accessible and adaptable. DOCX reflow is a genuine advantage for readers who need large text.

The mistake in each direction

Sending DOCX when you meant PDF. Your layout arrives broken and you never find out. This is the more common and more damaging error.

Sending PDF when they need to edit. They have to convert it back, which is lossy and annoying, because the structure was discarded when the PDF was made. If you know they’ll edit it, send both.

Which one is future-proof?

PDF, comfortably. It’s an ISO standard, and PDF/A exists specifically for long-term archiving — many public archives require it. PDFs made decades ago still open in current readers.

DOCX is also a published standard and isn’t going anywhere, but it depends on font availability and rendering engines to look right, and those change. For anything you want readable in twenty years, PDF.

Converting between them

• Word to PDF is straightforward. You’re going from structure to a fixed page, which is what PDF was built for. Almost nothing is lost.
• PDF to Word is genuinely hard. The structure has to be inferred from coordinates. Text-heavy documents convert well; complex layouts don’t.

The asymmetry is the whole story: it’s easy to throw structure away and hard to reconstruct it. Which is why, if a document might ever need editing again, you should keep the DOCX.

The practical rule

Work in DOCX. Send PDF. Keep both.