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What File Formats Work for Fax (and Which Don't) | SecurelyFax

PDF is the best format for online fax — it preserves layout, prints predictably on the recipient's machine, and supports multiple pages in one file. Images (JPG, PNG, HEIC) also work and are converted to PDF before sending. Word documents, spreadsheets, and password-protected PDFs need an extra step before they're faxable. Here's the full file-format guide.

File formats by faxability

Format Works? Notes
PDF Best Preferred. Multipage, predictable layout, smallest file.
JPG / JPEG Yes Single image per file. Converted to PDF before sending.
PNG Yes Same as JPG. Good for high-contrast scans of black-on-white pages.
HEIC / HEIF Yes iPhone default. Converted to PDF before sending.
TIFF Yes Multipage TIFF works; less common but supported.
WEBP / GIF / BMP Yes Less common image formats; converted before sending.
Password-protected PDF No Remove the password first or fax will fail.
Word (.doc, .docx) Not directly Save as PDF first, then fax the PDF.
Excel / Sheets (.xls, .xlsx) Not directly Save as PDF first, then fax the PDF.
RTF / TXT Not directly Save as PDF first, then fax the PDF.
HEIC + Live Photo Image part only Faxes the still image, not the motion.
ZIP archive No Open the archive first, then fax the document inside.

Why PDF is preferred

PDF was built for cross-system document exchange — it pins layout, fonts, and pagination so the page that lands on the recipient's machine looks like the page that left your computer. Fax transmits a black-and-white rendering, and PDF gives the sending system the clearest version of what to render. If the document is already a PDF, send the PDF — don't convert it to an image first.

Image considerations for fax

Fax is a black-and-white medium. Sharp, high-contrast images come through cleanly; dim photos of paper documents look like dim photos of paper documents. Some tips: photograph in good light, lay the document flat on a contrasting surface, fill the frame, and crop before sending. Most online fax services auto-convert images to PDF, but the source quality is what shows up on the recipient's side.

Password-protected PDFs

If your PDF requires a password to open, the fax service can't open it either — and the fax will fail. Remove the password before sending (Acrobat: File → Properties → Security → set Security Method to "No Security"). If you can't remove the password, ask the source for an unprotected copy. SecurelyFax never asks you for a PDF password.

Office documents (Word, Excel, etc.)

Save as PDF before faxing. Every modern office app has File → Save As → PDF, or File → Export → PDF. This gives the fax system a clean, faxable file with predictable layout. Don't try to fax the .docx directly — even if the service accepts it, the rendering can shift fonts or pagination in unexpected ways.

When in doubt: convert to PDF first

  1. 1
    Open the document
    In whichever app created it — Word, Pages, Excel, Numbers, Photos, etc.
  2. 2
    Choose File → Save As (or Export) → PDF
    Every modern app supports this. On mobile, the share sheet has "Print → Save as PDF" or similar.
  3. 3
    Pick the right page size
    US Letter for U.S. recipients. A4 for international. Most apps default correctly.
  4. 4
    Send the PDF through SecurelyFax
    Email, browser upload, or phone scan all work.
If a fax fails specifically because of file format, SecurelyFax surfaces a clear reason in the send result — and we don't charge for the failed attempt. Convert the file, send again.

Frequently asked questions

Can I fax a Word document?
Not directly — save it as a PDF first. Every modern Word app supports File → Save As → PDF, or File → Export → PDF.
Can I fax an iPhone photo?
Yes. HEIC and JPG images both work. SecurelyFax converts them to PDF automatically.
Will a password-protected PDF fax?
No. The fax system can't open a password-protected PDF, so the send will fail. Remove the password first.
Should I fax color or black-and-white?
Fax is a black-and-white medium. Color faxes are converted to black-and-white before transmission. Photographs with low contrast may come through unclear.
Is there a file-size limit?
Yes. SecurelyFax accepts files up to the platform's per-fax max upload size (shown on the send page). Very long documents may also exceed the recipient's machine capacity; split into smaller batches if needed.
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Last reviewed: 2026-05-30

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