The phrase "sign a PDF" hides two genuinely different things behind one everyday sentence, and it is worth being precise about which one you actually need, because the wrong choice can range from harmless to a real problem depending on the document. minipdftoosz's Add Signature tool does the first kind. Plenty of enterprise e-signature platforms exist specifically to do the second kind. They solve different problems, and neither is a drop-in replacement for the other.
What Add Signature does is straightforward and entirely visual: you draw a signature on a canvas — using signature_pad, an open-source library built specifically for capturing smooth, natural-looking handwritten strokes from a mouse, trackpad, or touchscreen — and the tool places that drawing as an image onto a page of your PDF, at a position and size you choose. The result looks exactly like a pen signature, because functionally it is one, just captured through a screen instead of on paper. It is the direct digital equivalent of printing a page, signing it with a pen, and scanning it back in, minus the printer and scanner.
A cryptographic digital signature is a different construction entirely. It uses public-key infrastructure: the signer holds a private key (often issued and vouched for by a certificate authority), and signing a document produces a mathematical signature over the document's content that can be verified against the signer's public certificate. Crucially, this kind of signature also proves the document has not been altered since signing — any change to even a single byte invalidates the signature. It carries an audit trail, a verifiable identity claim, and in many jurisdictions specific legal standing under e-signature law (frameworks like eIDAS in the EU or the ESIGN Act in the US draw real distinctions between signature tiers).
A drawn signature image has none of that infrastructure behind it. Nothing about a PDF with a drawn signature on it cryptographically proves who drew it, when, or that the surrounding pages have not been swapped out since. It is not tamper-evident. If someone later disputes having signed a document, a drawn signature offers roughly the same evidentiary weight as a scanned paper signature — which is to say, some, in many everyday and legal contexts, but nowhere near the strength of a properly executed digital signature with a certificate chain behind it.
For the large majority of everyday paperwork this distinction genuinely does not matter: internal approvals, informal agreements between people who already trust each other, personal document annotations, permission slips, acknowledgment forms — anywhere a handwritten signature has always been considered sufficient, a drawn signature captured digitally is equally sufficient, and considerably more convenient than printing and scanning. Freelancers and small businesses reach for tools like this constantly for exactly that reason.
Where the distinction does matter is anywhere a document specifically requires a certificate-based e-signature: many commercial contracts, real estate transactions, certain regulated filings, and any agreement where a counterparty's legal or compliance team has explicitly required it. In those cases, a dedicated e-signature service with proper PKI infrastructure behind it is the correct tool, and no amount of drawing carefully on a canvas substitutes for that. The honest rule of thumb: if you would have been comfortable with a plain pen-on-paper signature for this specific document, a drawn signature captured in your browser is equivalent. If your counterparty has specifically asked for a "digital signature" in the compliance sense, they mean the cryptographic kind, and you should reach for a service built for that instead.