How to sign a PDF online, on Mac, or on iPhone

Someone emails you a PDF and asks you to sign and send it back. There's no signing link, and opening the file doesn't make the next step obvious.

You can add your signature in a browser, in Preview on a Mac, or with the built-in tools on an iPhone. If the sender did provide a signing link, follow it instead of editing a downloaded copy. If their instructions mention a certificate or digital ID, you'll need a different signing process.

Disclaimer: This information is for general informational purposes only. This is not intended to be legal advice and should not be a substitute for professional legal advice. Consult a licensed attorney for legal advice or representation.

Key takeaways

• If the sender gave you a signing link, use it. Editing a downloaded copy can leave prepared fields or the original request incomplete.
• For an attached PDF, you can sign online, use Preview on a Mac, or use Markup on an iPhone.
• Drawing or typing your signature—or uploading a photo of it—can add a visible signature to the PDF. If the instructions require a certificate or digital ID, that visible signature alone won't be enough.
• Review the finished PDF before returning it, then keep the signed document and any confirmation you receive.

How do you sign a PDF?

Start with what the sender gave you:

• A signing link: Open the link and complete the prepared fields in the sender's signing workflow.‍
• A PDF attachment: Open it in an online PDF-signing tool if you want to sign in your browser.‍
• A PDF on your Mac: Use the signature tool in Preview.‍
• A PDF on your iPhone: Use the form-filling or Markup tools in a supported app.‍
• A certificate or digital ID requirement: Follow the sender’s instructions. A drawn, typed, or uploaded signature by itself won't meet the necessary requirements.

Whichever method you use, review the document before signing and complete every requested field, including signatures, initials, dates, or text fields. Open the finished PDF to make sure your entries appear correctly, then return or submit it as instructed and keep a copy.

If the sender created a signature request, use the original link. Editing a downloaded copy can leave that request unfinished.

How do you sign a PDF online?

If you received a PDF attachment rather than a signing link, an online PDF-signing tool lets you add your signature in a browser.

The controls vary by tool, but the process is usually:

1. Upload or select the PDF.
2. Choose the option to add a signature.
3. Draw your signature, type your name, or upload an image.
4. Place the signature in the correct field and complete any other required fields.
5. Review the document, then send the signed copy.
6. Download a copy for your records.

Open the completed PDF before closing the browser tab. Make sure your signature and other entries appear correctly and that you saved the signed document rather than the original.

Browser-based tools may upload your document to the service provider. Before using one for a sensitive or work document, check how the service stores, accesses, and deletes uploaded files. Follow any rules your employer or the document owner has about approved tools.

Need to prepare the PDF for somebody else instead? You can ⁠send a PDF for signature online with Dropbox Sign. Add the fields your recipient needs, send the request, and let them complete it from their browser. You can also use Dropbox Sign to ⁠sign and fill PDF documents.

How do you sign a PDF on a Mac?

If the PDF is on your Mac, Preview lets you add a signature without going to an online PDF-signing site.

1. Open the PDF in Preview.
2. Select Show Markup Toolbar, then select Sign.
3. Choose a saved signature or create one with your trackpad, your Mac's built-in camera, or a nearby iPhone or iPad.
4. Select the signature to add it to the PDF.
5. Drag it into position and use the handles to resize it.
6. Choose File > Save.

Preview saves signatures for reuse. If you have iCloud Drive turned on, your saved signatures are also available on your other Macs that use iCloud Drive.

These steps use the Markup tools in Preview to place a visible signature on the PDF. They don't create a certificate-based digital signature, so use a different method if the sender requires a certificate or digital ID.

Sign a PDF online

Upload the PDF, add signature fields, and send a shareable signing request from your browser—no Preview or Markup required.

Start signing

How do you sign a PDF on an iPhone?

If the PDF is on your iPhone, you can add a signature with the form-filling or Markup tools in a supported app.

1. Open the PDF. If prompted, open it in Files and tap Save.
2. Open the form-filling or Markup tools, tap Add, then tap Add Signature.
3. Sign your name with your finger, then tap Done.
4. Drag the signature into position and use the dots around it to resize it.
5. Review the document, then tap Share to send the completed copy. Tap Done to close it.

Your iPhone saves the signature for the next time you use Markup. You can also create and save more than one signature.

These steps add a visible signature with Apple’s form-filling or Markup tools. If the sender requires a certificate or digital ID, follow their instructions for certificate-based signing instead.

What should you do when someone sends a signature request?

A signature-request email takes you to a prepared signing workflow. The sender may have already placed signature, initial, date, checkbox, or text fields in the document.

Open the original signing link, review the document, and complete each required field. Finish the platform's confirmation or submission step so the request is recorded as complete. Don't edit a downloaded copy unless the sender asks you to.

If the request is unexpected, confirm it with the sender using a phone number, email address, or other contact method you already trust. If the link has expired or won't open, ask the sender to issue a new request.

After signing, keep the completed PDF or access link you receive, along with any confirmation or activity record provided by the platform.

Do you need an electronic signature or a certificate-based digital signature?

A drawn signature, typed name, uploaded signature image, or completed signature field can form part of an electronic-signature process.

A digital signature uses public-key cryptography. A private key creates the signature, and the corresponding public key verifies it and helps detect changes to the signed data. In certificate-based signing, a digital certificate connects the public key to an identified holder.

Check the wording in the request:

• If it provides a signing link or asks you to draw, type, upload, or click to add your signature, follow that electronic-signature workflow.
• If it requires a certificate, digital ID, certificate authority, or named trust provider, follow its certificate-based signing instructions. A visible signature by itself won't meet that requirement.
• If it doesn't specify a method, ask the sender what they will accept before changing the PDF or obtaining a certificate.

The federal E-SIGN Act defines an electronic signature as an electronic sound, symbol, or process connected to a record and executed or adopted with the intent to sign. It doesn't require public-key cryptography. A digital-signature process can therefore qualify as an electronic signature when a person uses it with the intent to sign.

For a broader comparison, see the types of electronic signatures.

Why can't you sign a PDF?

The fix depends on where the signing process stops.

The signing link doesn't work

The request may have expired, been canceled, or already been completed. Return to the original email and request a new link if the service offers that option. Otherwise, contact the sender. Adding a signature to an attached copy won't complete the original request.‍

You can't find a signature tool

Your current browser or PDF viewer may not support the signing method you need. Open the PDF in an app with form-filling or signature tools. If the PDF's security settings restrict filling or signing, ask the document owner for a version you are allowed to complete.

Certificate-based signing won't start

The signing software needs a digital ID and access to its private key. A certified PDF or a document that was locked after signing may also prevent further changes or signatures. Ask the sender which certificate, issuer, and application they accept before setting up a new digital ID.

How do you get signatures on a PDF with Dropbox Sign?

If you get signatures on PDFs regularly, a prepared signature request keeps everyone in one workflow instead of passing edited copies back and forth.

With Dropbox Sign, you can:

1. Upload the PDF.
2. Add the names and email addresses of the people who need to sign.
3. Place the signature, initial, date, checkbox, or text fields each person needs to complete.
4. Review the request and send it for signature.

Signers receive an email link and can complete the request in their browser without creating a Dropbox Sign account. You can check each request's status and send reminders while it's waiting for signatures.

If you send the same type of document repeatedly, Dropbox Sign templates let you prepare it once and use it for future requests. Template availability and limits depend on your plan.

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How do you add a signature to a PDF?

If the sender gave you a signing link, open it and complete the prepared signature field. For a standalone PDF, open it in an online signing tool or compatible PDF app, choose the signature tool, then draw, type, or upload your signature. Place it in the correct spot, review the PDF, and save or submit it.

How do you add a handwritten signature to a PDF?

You can draw your signature directly, upload a clear image of it, or capture a signature written on paper with a supported app. Preview on Mac supports the trackpad, camera, and a nearby iPhone or iPad. Markup on iPhone lets you sign with your finger.

How do you sign a PDF without uploading it?

Use a PDF app installed on your device instead of a browser-based signing service. Preview can add a signature on a Mac, while Markup can add one in supported iPhone apps.

The file may still sync online if it's stored in iCloud or another cloud service. Check where the PDF is saved if keeping it entirely on the device matters.

Why can't you digitally sign a PDF?

If you mean a certificate-based digital signature, your software may not have access to the required digital ID or private key. The PDF may also restrict additional changes, or an existing signature may have locked it.

Check the sender's certificate requirements and the instructions for your signing software. If the sender only needs a visible electronic signature, use the ordinary signature tool or the signing link they provided.

Is a signature image legally valid?

A signature image can qualify as an electronic signature under the E-SIGN Act when it's connected to the record and the signer adds or adopts it intending to sign. For transactions covered by the Act, a signature or contract generally cannot be denied legal effect solely because it's electronic.

That doesn't make every signature image or signed document enforceable. The type of document, applicable law, required formalities, and evidence of the signer's intent can matter. The E-SIGN Act also excludes certain records and transactions. Ask a lawyer about a particular document or requirement.

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