How to sign a PDF on your phone in under a minute

For most everyday paperwork, a rental form, a school permission slip, a freelance quote, "sign and return" means exactly that: put a signature that looks like yours on the last page and send the file back. You don't need a scanner for this, and you don't need to print anything.

Step by step

1. Save the PDF to your phone. In most mail apps, tap the attachment, then the share button, then Save to Files (iPhone) or Download (Android).
2. Open Sign PDF in your browser and choose the file.
3. Draw your signature in the box with your finger. Turn the phone sideways if the box feels cramped; you get a much smoother line.
4. Under Page, the default is the last page, which is right nine times out of ten. Choose A specific page if the signature line is elsewhere.
5. Pick a Position close to the signature line and adjust Width. Around 25 to 30 percent of the page width looks natural.
6. Press Sign PDF, download the file and attach it to your reply.

If the signature has to sit on a precise line

The nine preset positions are fine for most forms. When the line is somewhere awkward, say in the middle of a page next to a date field, use PDF Studio instead: open the PDF, go to Draw, sign directly on the page, then drag and resize the signature until it sits exactly on the line. You can add the date with a text box in the same place.

A better-looking signature

• Sign slowly. Fast strokes on glass come out jagged.
• Sign a sheet of white paper with a dark pen, take a photo in good light, and upload that image instead. It looks like ink because it is.
• Keep the result small. A signature that fills half the page looks fake even when it's real.

Is this legally valid?

For a lot of ordinary agreements, an image of your signature on a document you clearly sent is accepted. Some documents, though, require a certified digital signature: certain contracts, public tenders, some HR and banking forms. We wrote a separate piece on the difference between electronic and digital signatures; if the sender asks for a "qualified" or "certified" signature, this tool is not the right one.