How browser-based PDF signing works
When you drop a PDF into this page, two libraries go to work. Mozilla's pdf.js renders each page onto an HTML canvas so you can see where you're placing things. pdf-lib keeps the original PDF bytes in memory so that when you click Download, it can embed your signature images at the correct pixel coordinates, re-save the file, and hand it back to you. Neither library sends a byte of your PDF to a server.
This is genuinely different from almost every other "free PDF signer" on the internet. The usual pattern is: you upload your contract, their server processes it, they send back a download link, and your file now lives on their hard drive (and, often, in someone's logs). For a birthday card, who cares. For a lease, a medical release, a payroll form — it matters a lot. Running it in your browser is the only way to be sure.
The three ways to make a signature
- Draw — mouse, trackpad, or finger on a touchscreen. Good for phones and tablets.
- Type — pick from six cursive fonts. Good on laptops when you don't want to hand-draw.
- Upload — if you already have a scanned or phone-photo signature as a PNG or JPG, drop it in.
Tips for a convincing signature
Keep it small — real signatures are rarely bigger than an inch or two wide on paper. Don't stretch it to fit. Place it on the signature line, not below it. If there's a date field nearby, you can "sign" with another placement containing today's date (type mode + a non-cursive font works well).
Frequently asked
Is my PDF uploaded?
No. The PDF is decoded by pdf.js and re-written by pdf-lib, both running as JavaScript inside your browser tab. You can disconnect from the internet after the page loads and signing still works.
Is a signature added here legally binding?
In many jurisdictions, a visible, consented mark on a document is legally sufficient for everyday agreements — but it is not a qualified e-signature. It lacks the audit trail, identity check, and certificate-based tamper evidence that services like DocuSign and Adobe Sign provide, and that some contracts or regulations explicitly require. For documents where provenance matters, use one of those. For an internal form or a quick approval, Unfuss Sign is fine.
Can I add multiple signatures on multiple pages?
Yes. Once you "Use this signature," every click on any page drops another copy. The same is true for typed initials or a date — hit Use again to place more.
Why does my uploaded signature have a white background?
If you uploaded a JPG, it had no transparency to begin with. For a clean look, save your signature as a PNG with a transparent background — most phone apps that scan signatures give you this option. Or just place it on a region of the PDF that's already white.
Can I sign a password-protected PDF?
Not directly. Remove the open-password first (Preview or Acrobat both support this), sign, then re-apply a password if needed.
Will the rest of the PDF's content stay intact?
Yes. Adding a signature does not rasterise the PDF. Existing text stays selectable, links keep working, form fields remain fillable. The signature images are added as overlays on the correct pages.