Signing a PDF on your phone, without installing anything

The situation

Someone sends a contract as a PDF. You are not at a desk. Printing it, signing it, photographing it and sending the photo back works, and it produces a crooked grey scan that the other side has to squint at.

What the phone already does

On an iPhone, Files and Mail both open a PDF in Markup, and Markup can place a drawn signature. On Android the built-in viewer usually cannot, and whether Google Drive offers it depends on the version. Either way the result is a drawing on top of the page — fine for a delivery note, and nothing a system can verify later.

What a browser tool adds

A browser tool lets you place the same drawn signature with more control: pick the page, size it, add a date, initial every page of a long document. The one that matters is where the file goes. A site that uploads your PDF to its server to stamp it has your contract. A site that does the work in the page does not.

That is a question you can answer before you upload. Open the tool, turn off wifi and mobile data, and try to sign a file. If it still works, nothing is being sent anywhere.

Before it counts as signed

A drawn signature is a picture of a signature. For a tenancy agreement or a handover note that is usually what both sides expect. For anything where someone may later dispute who signed, you want a digital signature backed by a certificate — a different thing, covered in Chữ ký điện tử và chữ ký số.