How to add a digital signature to a PDF

Three ways to sign a PDF

Most people who search for a digital signature want the first method. They have a PDF and need their signature on it today.

The second method is a technical standard. It wraps the file in a cryptographic seal tied to a certificate.

Is a digital signature the same as an electronic signature?

No. An electronic signature is any sign of intent to sign a record. US law defines it as a sound, symbol or process attached to the record.

A digital signature is one kind of electronic signature. It uses a key pair and a certificate from a trusted authority.

Both can bind you to a contract. The ESIGN Act says a signature cannot lose legal effect only because it is electronic.

What changes is the proof. A certificate names the signer through the authority. A drawn signature relies on the record of who signed and when.

How to add a signature to a PDF for free

1. 1Open the tool. Use the free signer at the top of this page or go to Sign PDF.
2. 2Drop your PDF. Drag it into the box or choose it from your computer or phone.
3. 3Draw your signature. Tap «Draw my signature» and sign with your finger, mouse or pen.
4. 4Place it. Tap the spot on the page. Drag to move it and pull the corner to resize it.
5. 5Add the date. Use the date button for the signing date or the text button for your name.
6. 6Download it. Save the signed PDF. On a phone, use the brown bar at the bottom that says «Download signed PDF».

The signed file keeps its original name with «-signed» at the end. Your drawn signature stays saved on your device for next time.

What the free signature certificate adds

The box «Add signature certificate» comes checked. It adds one last page to your signed PDF.

• The name of the person who signed and an optional email
• The date and time from your device
• The file name and its number of pages
• The SHA-256 fingerprint of the original PDF

The fingerprint is a 64-character code. The same file always gives the same code. A change of one comma gives a different one.

Anyone can check later that the original did not change. They use the free signature verification tool with both files.

How to add a certificate-based digital signature

Some offices ask for a signature tied to a digital ID. You buy that ID from a certificate authority and install it on your computer.

1. 1Get a digital ID from a certificate authority your recipient accepts.
2. 2Install it in your PDF reader or your operating system keychain.
3. 3Open the PDF in a reader that supports certificate signatures.
4. 4Choose the certificate signing option and draw the signature box.
5. 5Pick your digital ID and enter its password or PIN.
6. 6Save the file. The reader seals it and records the certificate.

Ask the recipient first which certificate they accept. Each office trusts its own list of authorities.

How to check a signature on a PDF

A certificate signature shows a panel in most PDF readers. The panel says whether the file changed after signing.

A drawn signature with a SignSolú certificate gets checked another way. Drop the original PDF and the signed PDF into the verification tool.

The tool computes the fingerprint of the original on your device. It compares that code with the one printed on the certificate.

• «The fingerprint matches.» The original did not change since it was signed.
• «The fingerprint does not match.» The original you dropped is not the one that was signed.

Your PDF never leaves your device

The free tool opens and signs the file inside your browser. Nothing is uploaded to a server.

Close the tab and the file is gone from the page. Your drawn signature stays on this device until you delete it.

Use «Forget my data on this device» to erase it. That option sits next to the tool.

What a signed PDF should include

A signature alone proves little. The page around it carries the rest of the evidence.

• The full name of each signer, written near the signature
• The date of signing, added with the date button
• Initials on pages that change terms, such as prices or dates
• A certificate page with the fingerprint of the original file
• The same file name you shared with the other party

Keep the original PDF and the signed PDF in the same folder. Name them so anyone can match them later.

Common mistakes when signing a PDF

• Pasting a photo of your signature. A loose image has no record of who placed it or when.
• Signing the wrong version. Check the file name and the last edit before you sign.
• Skipping the date. Add the signing date next to your signature with the date button.
• Sending only the signed copy. Keep the original too. The fingerprint check needs both files.
• Editing after signing. Any change after signing breaks the fingerprint match.
• Forgetting initials. Some contracts ask for initials on each page. Use the initials button for those.

Fix these before you send the PDF. Each one is easier to prevent than to explain later.

Which method should you choose?

Start with the document and the person who will receive it. The answer usually follows from there.

A lease, an NDA or a service agreement works with a drawn signature. Add the certificate page so anyone can check the file later.

A tax filing or a public tender may name a certificate type. In that case follow the instructions of that office.

A will or a court filing follows its own rules. Check those rules before you sign anything electronically.

When two or more people must sign, send it from an account. Each signer gets a link and SignSolú keeps the record.

Is a signed PDF legally valid?

Yes, in most cases. The ESIGN Act covers transactions in interstate or foreign commerce. States have their own electronic transaction laws as well.

Some records stay outside the ESIGN Act. Wills, family law matters and court documents are on that list.

Our guide to wet signatures lists every exception. It also covers how to handle each one.

When someone else has to sign

Send the PDF from a free SignSolú account. The other person gets a link by WhatsApp or email. They open it on their phone and tap the brown bar that says «Sign as …». You get the signed PDF back with a certificate that SignSolú timestamps. Your first ten documents are free.

When the PDF needs several signers

Sign your part first and download the PDF. Then pass that signed file to the next person.

Each signer places a signature and adds the date. The certificate page lists every person who signed on that device.

For signers in other cities, send it from an account. Each one gets a link and SignSolú collects the signatures in one file.

Sources

• 15 U.S.C. 7001, general rule of validity on govinfo.gov
• 15 U.S.C. 7006, definitions on govinfo.gov
• Public Law 106-229, the ESIGN Act as passed on govinfo.gov