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PDF is the safest file type to fax: it holds its layout on any system, and every fax service accepts it. Word documents, spreadsheets, and photos can all be faxed too, but each goes through a conversion to black-and-white first, which is where formatting breaks, tiny text turns to mush, and colors vanish. If the document matters, convert it to PDF yourself before sending.
| File type | How it faxes | Watch out for |
|---|---|---|
| Best choice: layout is fixed, fonts are embedded, converts cleanly | Password-protected PDFs often fail at the conversion step | |
| Word (.docx) | Works, but the service renders it first, so pagination and fonts can shift | Export to PDF yourself instead of trusting the service's renderer |
| Excel / spreadsheets | Wide sheets get shrunk to fit, which can make text unreadable | Set the print area and fit-to-page in the spreadsheet before exporting |
| Photos (JPG, PNG) | Converted to dithered black-and-white; fine for ID-style images, poor for detail | High-contrast originals fax far better than dark or washed-out ones |
| Scanned pages | Usually fine if the scan is clean; crooked or shadowed scans fax badly | Scan at a reasonable resolution and check the scan yourself first |
A PDF describes exactly where every character sits on the page, with the fonts baked in. When a fax service converts your file, it is really doing two steps: render the file to an image, then convert that image to the black-and-white format fax machines understand. PDF skips the risky first step because it already looks the same everywhere. Word documents, by contrast, get rendered by whatever software the fax service happens to run, which may substitute fonts, reflow paragraphs, and repaginate. If your contract arrives with the signature block pushed onto a new page, that rendering step is usually why.
They survive, but they need preparation. For spreadsheets, the killer is width: a sheet designed for a wide monitor gets squeezed onto a letter-size page, and 8-point text squeezed to half size becomes gray noise. Fix it before you export: set a print area, choose fit-to-one-page-wide, and bump the font size. For Word documents, export to PDF from Word itself rather than letting the fax service do the conversion. You see exactly what the recipient will get, and the page count you approve (LetterAgent verifies the page count up front as part of the quote) matches the document you checked.
Photos fax as coarse black-and-white images, which is fine for a driver's license photo or a damage photo where the outline matters, and hopeless for anything where color or fine detail carries the meaning. Scans are the more common case, and scan quality decides everything: a straight, well-lit scan at a normal resolution faxes cleanly, while a crooked phone photo of a page taken in bad light produces a fax nobody can read. One specific trap: yellow highlighter, the classic "look here" mark, often disappears completely in black-and-white conversion. If highlighting carries meaning, replace it with bold text or a box drawn in black before you send.
A few. Password-protected PDFs frequently fail because the conversion step cannot open them: remove the password or print and re-scan before sending. Very large files can time out during upload or conversion, so keep documents to a reasonable size. And anything that is not really a document, a zip archive, an executable, a video, cannot be faxed at all: fax only carries page images. When in doubt, the rule is simple: if you can print it and read the printout, you can fax it; the fax is just a remote printout.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
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