The format question only has one wrong default: assuming whatever the file already is in is the right thing to send. Almost every document benefits from a moment’s thought about the format before it goes out, and for most of them, the answer is the same.
Is the recipient reading it, or editing it?
That single question decides almost everything.
Reading only — a CV, an invoice, a signed contract, a report, meeting notes, a flyer — means send a PDF, not the source file. A PDF locks in the layout so it looks the same on their screen as yours, opens on any device without needing the software that made it, can’t be accidentally edited or overwritten in transit, and reads as more finished than a native file arriving in someone’s inbox. Word document → Word to PDF; spreadsheet → Excel to PDF; slide deck being shared to read rather than present from → PowerPoint to PDF.
Editing is the point — someone needs to add their section, adjust the numbers, or leave tracked changes — send the native .docx or .xlsx instead. A PDF actively gets in the way here, since editing it requires converting it back first.
There’s a second reason to default to PDF even when you’re both reading from the same source software: rendering. A .docx built with a recent Word feature can look wrong, or refuse to open, in an older version of Word, a competing word processor, or a mobile app with partial format support. A PDF sidesteps that entirely — the rendering was already decided and locked in before you hit send. This matters most for a recipient whose setup you don’t control: a client, an application portal, a stranger.
When even a PDF is more than you need
If the destination doesn’t display documents at all — a social media post, a WhatsApp status, a webpage that only accepts image uploads — converting to an image is the actual right call, not a downgrade. See How to Post a PDF on Instagram, LinkedIn, or WhatsApp Status.
Before you actually hit send
Three things are worth a second look regardless of format:
- Over your email provider’s attachment limit (commonly 20–25 MB)? Compress the PDF rather than defaulting to a cloud storage link — a link the recipient has to click and possibly request access to is friction a straightforward attachment avoids.
- Sensitive content — a payslip, an ID scan, a medical letter, a signed contract? Format choice alone doesn’t protect it. How to Email Sensitive Documents Safely covers encrypting the file and sending the password through a separate channel.
- A spreadsheet you don’t want edited or resorted, even by someone well-meaning? Share a Spreadsheet Nobody Can Change covers why PDF is usually the safer send there too.
Converting a Word file is the most common case by a distance — Convert Word to PDF Online for Free is the plain walkthrough, and Word to PDF: Keep Hyperlinks, Comments, and Track Changes covers what survives the conversion and what quietly gets flattened out of it.
Whichever format you’re starting from, Word to PDF, Excel to PDF, and PowerPoint to PDF all work the same way — free, no sign-up, and nothing left on our servers afterward.