Preparing a PDF for fax: resolution, contrast and page count

Short answer: what reaches your recipient is a two-tone image with no grey at all, sampled at 204 × 196 dpi (fine mode) or 204 × 98 dpi (standard mode). Anything pale, lightly coloured, very small or very thin may vanish. Aim for an upright A4 PDF, dark characters on white, body text of 11 pt or more, clean scans at 200 or 300 dpi, and not a single spare page. On FaxTelecom a single page is free; from the second one, a flat €3.99 incl. VAT covers the whole document.

What happens to your PDF between upload and printout

Your file doesn't travel as it is. It is first converted into a series of images, one per page. Each A4 page becomes a grid about 1,728 dots wide. Every dot is either black or white: Group 3 fax knows nothing else. Those images are compressed, sent down the phone line, then printed or stored by the machine at the other end. The full mechanism is laid out on our page about how faxing works.

So the right question isn't "does my PDF look good?" but "will it still read once reduced to pure black on pure white at around 200 dpi?".

Standard, fine, superfine: fax resolutions

Resolution is negotiated between the two machines at the start of every call, and an old fax machine can force standard mode. Design your document for fine mode, then make sure it would still make sense in standard, where letter height is cut in half.

Contrast comes first

The switch to black and white works with a threshold: each dot lighter than a given level turns white, the rest turn black. That has direct consequences:

• Grey text is text at risk. Mid-grey can come out dotted, light grey can disappear completely. Set all text to black.
• No coloured backgrounds or watermarks. A grey diagonal "CONFIDENTIAL" becomes a cloud of specks over your words.
• Zebra-striped tables. Shading every other row looks great on screen and turns into a pattern that scrambles the figures. Swap it for thin but black borders.
• Highlighter. Yellow evaporates; other colours can black out the highlighted word. Use bold or underline instead.

Fonts and layout

• 11 pt minimum for body text, never below 9 pt for footnotes.
• Regular or bold weights. "Light" and "Thin" fonts lose whole strokes; condensed fonts make letters touch.
• Margins of at least 1 cm. Many fax machines trim a few millimetres off each edge, so a header hugging the paper's edge may not arrive.
• Portrait A4. A landscape page is often shrunk to fit the width, which makes everything smaller. US Letter is fine for Canada, but avoid mixing sizes in one PDF.
• "2/5" page numbers. The recipient can see at a glance that nothing is missing.
• Fillable forms. Field contents don't always survive conversion. Flatten the file first: open it and choose "Print to PDF".

Scanning a paper document with a phone

You don't need a scanner. A phone will do, as long as you go about it methodically:

1. Lay the sheet flat on a dark, plain surface so the edges stand out.
2. Light it from the front, in daylight, without your hand or the phone casting a shadow.
3. Use a "scan" mode rather than the camera: Notes on iPhone, Google Drive's scan feature on Android, or a dedicated app. They straighten the perspective and crop automatically.
4. Pick the black and white or greyscale filter, never "colour" or "photo".
5. Check the crop, then export as PDF, all pages in one file.

Our page on faxing from a phone walks through the whole send from a mobile, from scan to tracking.

Signatures, stamps and seals

A signature in light-blue ballpoint is one of the most fragile things you can put on a fax. Sign with a black or dark-blue felt pen, using a firm stroke. For a signature inserted as an image, put it on a white background (a transparent PNG on a shaded area becomes a dark block) and make it at least 3 to 4 cm wide.

Red or purple stamps come out as dotted grey at best, unreadable at worst. Press hard, ink the stamp well, then test: print the page in black and white on your own printer. If the stamp survives a monochrome print, it will survive the fax.

Bear in mind that a signature received by fax remains a copy. What it is worth as evidence is covered on our page about the legal value of fax.

Colours, charts and photos

Photos turn into dot patterns (dithering): fine for a face, far less so for an ID card. If you must send an identity document, scan it in greyscale, enlarged on the page, with high contrast. For charts, tell series apart by line style (solid, dotted, dashed) and labels, never by colour alone.

File size

FaxTelecom accepts PDFs up to 100 MB, but a heavier file doesn't arrive any sharper: everything ends up at roughly 200 dpi in black and white. A twenty-page colour scan at 600 dpi is bulky, slow to upload from a phone, and gains you nothing. A few benchmarks:

• Text exported from a word processor: a few dozen kilobytes per page.
• Monochrome page scanned at 300 dpi: often under 200 KB.
• File too big: use your PDF reader's size-reduction option (Preview on Mac has a dedicated filter).
• Password-protected PDF: remove the protection, or the document may not be convertible.

Page count and price

FaxTelecom's pricing fits in two lines: a one-page PDF is sent free, with no quota; anything longer is billed €3.99 incl. VAT as a flat fee, whether it runs to two pages or forty. Two practical consequences follow.

• Hunt down blank pages. A duplex scan of a sheet printed on one side adds an empty back page, and that empty page turns a free send into a paid one. Delete it before confirming.
• Don't cram to save money. Past two pages the price no longer moves. Four readable pages beat two pages set in 7 pt.

There's also no need to add your own cover page to the PDF: the form builds one from the sender, recipient, subject and your message. To fill it in well, read our article on fax cover page best practices.

Pre-send checklist

If the page passes that monochrome print test, it will arrive legible at the other end.