Add Signature to PDF — Sign Online

How Add Signature Works

Technically, signing a PDF this way is an image compositing operation, not a cryptographic one. When you draw on the canvas, the browser captures your pen strokes as a path and rasterizes it into an image. When you type your name instead, the tool renders it using a cursive-style font onto a canvas and captures that as an image too. Either way, the result is a small PNG with a transparent background. That image is then embedded into the PDF's object structure and drawn onto the target page's content stream at the X/Y coordinates you specify — mechanically the same process as embedding any other image onto a page, just with a signature-shaped graphic instead of a photo or logo.

That distinction matters because it sets expectations correctly. A cryptographic digital signature — the kind used in formal document-signing platforms — embeds a signed hash of the document along with a certificate, so any later tampering invalidates the signature and the identity of the signer is verifiable. This tool doesn't do that. It's the digital equivalent of signing a printout: a visual mark that communicates approval or acknowledgment, appropriate for internal forms, draft sign-offs, personal letters, or any document where a scanned wet-ink signature would have been acceptable, but not for contracts requiring legal non-repudiation.

Because the underlying mechanism is image placement, this tool is closely related to Add Image to PDF — the difference is purely the source of the image and the drawing interface built around capturing handwriting. It's also often used alongside Flatten PDF: if a document has fillable form fields that were completed and then signed, flattening afterward locks both the filled-in values and the signature into static page content so the finished document can't be accidentally edited again.

A few practical notes: drawing with a mouse tends to produce jagged, unnatural-looking signatures since a mouse lacks the pressure and continuous-motion feedback of a pen; a touchscreen or stylus gives noticeably better results. Typed signatures avoid that problem entirely by using a consistent font, at the cost of looking less personal. And since placement is per-page and per-operation, signing a multi-page contract that needs initials on every page currently means repeating the process once for each page.