The Difference Between a Visual Signature and a Digital Signature on Mac
A visual signature is an image of your handwritten signature placed on a PDF page. It looks like a signature but provides no cryptographic verification of your identity or the document integrity. A Digital Signature is a cryptographic seal that verifies both who signed the document and that the document has not been modified since signing. A digital signature is backed by a digital certificate issued by a trusted certificate authority.
For most personal and business documents on Mac, a visual signature created in Preview and placed on the document is sufficient. The recipient sees your signature and accepts it as evidence of your agreement or approval. For documents that require cryptographic verification, such as government filings, regulated financial documents, and legal submissions that specify digital signatures, a certificate-based digital signature is required.
The Sign PDF capability on Mac spans both types of signatures. Preview handles visual signatures elegantly. For digital signatures, the Mac Keychain Access application manages digital certificates, and Preview and other Mac PDF applications can use those certificates to apply certified digital signatures.
The Mac PDF ecosystem provides several paths to digital signatures. The built-in tools cover basic signing needs. Third-party applications provide additional features for managing certificates and applying signatures in compliance with specific regulatory standards.
Creating and Using a Visual Signature in Preview on Mac
Open Preview. Go to the Tools menu, select Annotate, and choose Signature, or click the Markup toolbar button and select the Signature tool. Click Create Signature. You have two options for creating the signature. Click Trackpad to draw your signature on the Mac trackpad with your finger. Press any key when finished. Or click Camera to sign a white piece of paper and hold it up to the Mac camera. The camera captures your signature as a clean image with a transparent background.
Preview saves your signature for future use. Once created, the signature appears in the Signature menu whenever you open the Markup toolbar in Preview. You can create multiple signatures, such as a full signature and initials, and select the appropriate one for each document.
To sign a PDF, open it in Preview, click the Markup toolbar button, select the Signature tool, and click the signature you want to use. The signature appears on the document. Drag it to position it over the signature line. Use the corner handles to resize it. The signature is placed as an annotation on the PDF page.
Save the signed PDF. Preview saves the signature as part of the document. The signature is a visual annotation. It is not a certified digital signature. It does not provide cryptographic verification. For documents that require certified digital signatures, use the digital certificate method described next.
Adding a Certified Digital Signature to a PDF on Mac
Obtain a digital certificate. For personal use, you can create a self-signed certificate using Keychain Access on Mac. Open Keychain Access from the Utilities folder, go to Keychain Access, Certificate Assistant, and select Create a Certificate. Follow the assistant to create a self-signed certificate. Self-signed certificates provide cryptographic verification but are not issued by a trusted authority. Recipients may see a warning that the certificate is not trusted.
For professional or legal use, obtain a certificate from a trusted certificate authority. Organizations like GlobalSign, DigiCert, and Entrust issue digital certificates for document signing. The certificate authority verifies your identity before issuing the certificate, and the certificate chains to a trusted root authority that PDF readers recognize automatically.
Install the certificate in your Mac Keychain. Double-click the certificate file and Keychain Access imports it. The certificate appears in your login keychain under the My Certificates category.
Open the PDF in Preview. Go to Tools, Annotate, Signature, and you should see your digital certificate listed as a signing option. Select the certificate, click on the document where you want to place the signature, and Preview applies the certified digital signature. The signature includes your name, the certificate information, and the date and time of signing.
WukongPDF's signature tools support both visual signatures and certificate-based digital signatures through a browser interface. Upload the PDF, select your signing method, and apply the signature. The browser-based approach works on Mac and other platforms.
Verifying a Digital Signature on a PDF Received from Someone Else
Open the signed PDF in Preview. A blue banner or a signature panel indicates the document contains a digital signature. Click the signature or the signature panel to view the signature details. The panel shows who signed the document, the certificate authority that issued the certificate, and whether the signature is valid.
A valid signature means the document has not been modified since it was signed and the signer certificate was valid at the time of signing. An invalid signature means the document was modified after signing or the certificate has been revoked or expired.
If the signature shows as not trusted, the certificate may be self-signed or issued by a certificate authority not recognized by your Mac. You can manually trust the certificate by adding it to your keychain, or you can ask the signer to provide a certificate from a recognized authority.
Preview displays a warning if you attempt to modify a digitally signed PDF. Any modification, including adding annotations, invalidates the digital signature. If you need to annotate a digitally signed document, save a copy first.
A digital signature on a PDF carries legal weight that a visual signature image does not. Under the ESIGN Act in the United States and eIDAS in the European Union, advanced electronic signatures that are uniquely linked to the signer and capable of identifying the signer carry the same legal effect as handwritten signatures. Certificate-based digital signatures meet these requirements.
For Mac users in regulated industries, the combination of Preview for everyday signing and Keychain Access for certificate management provides a complete signing toolkit without third-party software. The tools are built into the operating system, maintained by Apple security updates, and compatible with industry-standard digital signature formats.
Before applying a certified digital signature to an important document, verify that your certificate is valid and trusted. Open Keychain Access, find your certificate, and check that it is not expired and that it chains to a trusted root certificate. An expired or untrusted certificate produces a signature that recipients see as invalid or not trusted.
Multiple signatures can be applied to the same PDF, each in a designated signature field. A contract can have a buyer signature field and a seller signature field. Each party signs independently, and both signatures remain valid as long as the document is not modified between signatures.
Digital signatures include a timestamp from the signer computer. This timestamp provides evidence of when the document was signed. For documents where the signing time is legally significant, ensure your computer clock is accurate before applying the signature.
If you receive a digitally signed PDF and need to add your own signature, do not modify any other content in the document. Adding text, annotations, or even scrolling through form fields can invalidate the existing signatures. Apply only your signature in the designated field.
The Preview application on Mac can display digital signature validity information. Click the signature on a signed PDF, and Preview shows whether the signature is valid, who signed, and when. This built-in verification works for signatures created with certificates from recognized authorities.
Digital signature workflows on Mac integrate with Apple Mail and other email clients. You can sign a PDF and attach it to an email reply directly from Preview, without saving the signed file separately and then attaching it manually.
Self-signed certificates are adequate for internal document workflows where all parties trust the certificate source. For external documents shared with parties outside your organization, certificates from recognized authorities are necessary for the signatures to display as trusted.
The Mac Keychain securely stores your digital certificates and private keys. The private key never leaves your keychain. When you apply a digital signature, the signing operation uses the private key locally. The resulting signature can be verified by anyone with the corresponding public certificate.
The digital signature appearance on the PDF page can be customized. You can display your name, the date, the certificate issuer, and a signature image, or any combination of these elements. The visual appearance is independent of the cryptographic signature validity.
Preview can apply signatures to specific pages or to all pages in a document. Applying a signature to a multi-page contract typically means signing only the signature page, not every page of the document.
The Preview signature tool can also add text alongside your signature, including your printed name, title, organization, and the date. This text information completes the signature block and provides context for the recipient.
The ability to digitally sign PDFs on Mac without purchasing additional software makes document signing accessible to every Mac user. The built-in tools handle the signing needs of individuals and small businesses effectively.
Digital signatures on Mac are compatible with PDF readers on all platforms, so a document signed on Mac can be verified on Windows, Linux, iOS, and Android without compatibility issues.