How to Sign a PDF in Adobe Acrobat

Signing a PDF is the final step of many workflows — a contract, a consent form, an invoice approval. Adobe Acrobat supports two kinds of signatures: electronic signatures via the Fill & Sign tool (a picture of your signature placed on the page) and digital signatures via the Certificates tool (a cryptographic signature backed by a digital ID). This guide walks through both in Acrobat DC 2024 and later, explains the difference, and is honest about what IXPDF can and cannot do today.

Electronic vs digital signatures — the key difference

The two are often confused, but they are very different things:

• Electronic signature: a visual mark — a typed name, a drawn signature, or an uploaded image — placed on the page. It shows intent to sign, but it has no cryptographic protection. Anyone could copy the image and paste it into another document. Legally valid in many jurisdictions (US ESIGN/UETA, EU eIDAS) for many use cases, but the proof is the surrounding process (audit trail, identity verification), not the mark itself.
• Digital signature: a cryptographic operation using a digital ID (certificate + private key). It binds the signature to the document's exact bytes — any change after signing invalidates the signature. Verifiable by anyone with the signer's public certificate. Stronger proof, but requires a digital ID (self-signed or from a CA).

Use an electronic signature for everyday signing where the trust comes from the relationship (an internal approval, a simple agreement). Use a digital signature when you need cryptographic proof of who signed and that the document was not changed — legal filings, regulated industries, cross-border contracts.

Method 1: Fill & Sign (electronic, free in Reader)

1. Open your PDF in Adobe Acrobat (Pro, Standard, or the free Reader all work).
2. Go to Tools → Fill & Sign, or clickFill & Sign in the right-hand pane.
3. Click Sign at the top, then Add Signature (or Add Initials).
4. Choose how to create the signature:
   • Type: enter your name; Acrobat renders it in a script-like font.
   • Draw: draw with your mouse or trackpad.
   • Image: upload a photo of your signature on paper.
5. Click Apply. The signature appears as a movable stamp. Drag it to the right place on the page; resize by dragging the corner.
6. (Optional) Add text: use the Add Texttool to fill in date, name, or other fields before signing.
7. Choose File → Save to write the signed PDF. The signature is now part of the page.

Fill & Sign also lets you fill form fields, check checkboxes, and add crossmarks — useful for signed forms.

Method 2: Certificates (digital signature, Pro/Standard)

1. Open your PDF in Adobe Acrobat Pro or Standard.
2. Go to Tools → Certificates. The Certificates panel opens.
3. Click Digitally Sign. If the PDF has no signature field, Acrobat prompts you to drag a rectangle where the signature should appear.
4. If you have no digital ID, Acrobat walks you through creating a self-signed one: enter your name, organization, email, and a password for the private key. For higher assurance, load a certificate from a CA (DigiCert, GlobalSign, etc.) or a hardware token.
5. Choose appearance options — show your name, reason for signing, date, location, and a signature image. Click Sign.
6. Save the signed PDF. Acrobat writes a cryptographic signature over the document bytes. The signature panel shows "Signature is valid" if the document has not been modified since.

Verifying a signature

Open the signed PDF in Acrobat and look at the signature panel (left side). It reports whether the signature is valid, who signed, when, and whether the document was modified after signing. For digital signatures, it also checks the certificate chain against trusted roots. If the signature is invalid, do not trust the document.

Common mistakes

• Using an electronic signature when a digital one is required. A picture of your signature has no cryptographic proof. If the counterparty requires a digital signature, use Certificates, not Fill & Sign.
• Editing the PDF after signing. Any edit invalidates a digital signature. Sign last, after all edits are final.
• Losing the digital ID password. Without it, you cannot sign with that ID again. Store it in a password manager.
• Using a self-signed ID for high-assurance use cases.Self-signed IDs prove the document was not changed, but not who signed it. For external contracts, use a CA-issued certificate.
• Assuming an electronic signature is tamper-proof.The signature image can be copied. The trust comes from the process, not the image.