BASALT · JOURNAL
Signing a PDF, and the two things called a signature
The word signature covers two unrelated things in PDF, and confusing them causes both wasted effort and misplaced confidence.
A drawn signature
A picture of your handwriting placed on the page. It proves nothing cryptographically and is trivially copied by anyone with the document.
It is also what the overwhelming majority of signing requests actually want. Most documents that ask for a signature want a visual mark indicating assent, and the legal weight comes from context, intent and surrounding process rather than from the image.
A digital signature
A cryptographic operation binding the document's contents to a certificate. It proves that the document has not changed since signing, and it identifies the signer to the extent that the certificate's issuance was trustworthy.
This is a genuinely different thing. It requires a certificate, and its value depends entirely on how that certificate was issued and whether the verifier trusts the chain.
Which you need
For a contract between parties who know each other, an invoice, an engagement letter, or most routine business documents, a drawn signature is what is being asked for.
For anything with a compliance requirement naming digital signatures, for documents that will be verified by an automated system, and for filings where the court or registry specifies it, you need the cryptographic kind and the drawn one will not do.
Acrobat handles both and integrates with certificate authorities and enterprise signing infrastructure. If your requirement is the second kind, that infrastructure matters.
Getting a clean drawn signature
The practical difficulty is usually not signing but producing a clean image. A photograph of a signature on paper carries the paper: grey background, shadows, and a rectangle that looks wrong on a white page.
Lifting the background off a photographed signature so only the ink remains is the step that makes the result look native to the document rather than pasted on.
What a signature does not do
Neither kind protects the rest of the document. A signed PDF can still carry metadata, attachments and hidden content, and signing a document that was never sanitised simply produces a signed document with the same leaks.
Frequently asked questions
What is the difference between a drawn signature and a digital signature?
A drawn signature is an image of handwriting placed on the page, proving nothing cryptographically. A digital signature is a cryptographic operation binding the document contents to a certificate, proving the file has not changed since signing and identifying the signer to the extent the certificate is trustworthy.
Do I need a cryptographic signature for most documents?
Usually not. Most signing requests want a visual mark of assent, and the legal weight comes from context and intent. Cryptographic signatures are needed where a compliance rule, an automated verifier or a filing requirement specifies them.
How do I get a clean signature image from a photo?
Lift the background away so only the ink remains. A photograph carries the paper with it, producing a grey rectangle that looks pasted on rather than signed.
Does signing a PDF make it secure?
No. A signature attests to the document's integrity from that point onward. It does not remove metadata, attachments or hidden content, so signing an unsanitised document simply signs the leaks along with everything else.
Doing it in Basalt
Basalt is a native macOS PDF toolkit with eighteen tools in one window: merge, split, compress, OCR, Bates numbering, privilege logs, forms, signing, watermarks, comparison and more. Redaction destroys content rather than covering it, and an independent verifier re-opens every written file and proves the material is gone before the file is saved. If it cannot prove it, nothing is written. A one time $29 licence covers up to three Macs, it is free for the first 24 hours, there is no account, and the engine holds no network entitlement at all, which macOS enforces at the code-signature level. Download it at basaltformac.com.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.