How to make a PDF easy to read on a phone
Whatever you send — a notice to parents, a price list to customers, a report to a manager — there is a good chance it will be opened on a phone, often over mobile data. A PDF keeps its page layout exactly, which is its strength on paper and its weakness on a small screen: the reader has to zoom and pan around a page designed for A4. A few changes make that much easier.
Keep every page upright
A page scanned or photographed sideways is annoying on a computer and much worse on a phone, where turning the screen also changes the zoom. Before sending, scroll through and turn any sideways or upside-down pages the right way up, and make the change in the file itself so it stays turned for everyone who opens it.
A landscape table in the middle of a portrait document is fine — it should simply be stored the right way up for reading, even if that means turning the phone.
Trim wide margins
Phones fit the whole page width to the screen. Wide empty margins, a scanner's grey border or the blank space around a small scanned receipt all make the actual content smaller. Cropping them away makes the same text larger on the screen without changing a word.
Cropping hides the trimmed area rather than deleting it, so it is a display change, not a way to remove private information — use redaction for that.
Use real text, at a readable size
Text that is real text stays sharp when zoomed and can be searched and copied. A scanned page is a picture: zooming in on a phone reveals blur, and the reader cannot search it. If you are sending a scan, adding a text layer with OCR at least makes it searchable.
If you are creating the document, body text of about 11 to 12 points and a single column read far better on a phone than small text in two or three columns, which forces the reader to pan down one column and back up for the next.
Mind the file size, then check on a phone
A 25 MB PDF of phone photos can take a long time to open on mobile data and may not be downloaded at all. Compressing photographs to a sensible resolution usually makes the file several times smaller without a visible difference on a phone screen.
Before sending it widely, open the final file on your own phone. Read the first page without zooming, find the smallest text, and try a link or two. If you have to zoom to read ordinary text, your readers will too.