Add a handwritten-style signature to a PDF. Draw it with the mouse or a touchscreen, type it and pick a script face, or upload an image of your signature, then position it where it belongs on the page. This produces a visible signature - the electronic equivalent of signing a printout - which is what most everyday agreements and forms ask for.
In many jurisdictions a visible electronic signature is accepted for ordinary agreements, but it depends on your local law and on what the document requires. Where proof of identity and tamper-evidence is needed, a digital certificate signature is the stronger form.
This adds a picture of a signature. Certificate Sign applies a cryptographic signature bound to a certificate, which proves who signed and reveals whether the file has been altered since. They solve different problems and can be combined.
An image signature can be copied, which is precisely the weakness a certificate signature removes. Flatten the file afterwards to make it slightly harder, and use a certificate where the risk matters.
Files are uploaded over an encrypted connection and processed on CoonTool's own server, not in your browser. The working copy is deleted automatically once the job is done, and in any case within 24 hours. Nothing is stored permanently and no account is required.