The fastest way depends on what you already have

You can digitally sign a PDF using software you likely already own — Adobe Reader (free), Microsoft Word, or your web browser. If you need a legally binding signature for contracts or official documents, you will need to use a service that creates a digital certificate, which proves your identity. If the signature just needs to show you approved or reviewed the document, you can sign it in seconds with any PDF tool.

The difference matters because a certificate-based signature is harder to forge and holds up in court, while a straightforward signature is just a mark that says you opened the file. Most everyday documents — internal approvals, feedback forms, personal agreements — do not need a certificate. Contracts, loan documents, and anything filed with a government agency usually do.

Key Takeaways

  • Adobe Reader and Microsoft Word let you sign PDFs for free without a certificate, and the signature appears as a visible mark on the document.
  • DocuSign, Adobe Sign, and similar services create legally binding signatures by verifying your identity, but they charge a monthly fee or per-signature cost.
  • On a phone or tablet, you can sign by drawing your signature on the screen, taking a photo of your handwritten signature, or typing your name — all without special software.
  • A document signed without a certificate is not legally binding in the same way a certified signature is, so check what the recipient actually needs before you sign.
  • Once you sign a PDF, the signature is locked into the file and cannot be removed or altered without breaking the document's integrity.

Signing a PDF in Adobe Reader (free, no certificate)

Open the PDF in Adobe Reader on your computer. Click the Fill & Sign tool in the right panel, or go to Tools > Fill & Sign. Click the signature icon (looks like a pen) and then click where you want your signature to appear on the page.

Adobe will ask you to create a signature. You can draw one with your mouse or trackpad, type your name, or upload an image of your handwritten signature. Once you create it, Adobe saves it so you can use the same signature on future PDFs without redrawing it. After you place the signature, save the file. The signature is now part of the PDF and will appear when anyone opens it.

This method is fast and free, but the signature is not legally binding — it is just a visual mark. Use it for internal documents, drafts, or anything where you just need to show you reviewed the file.

Signing a PDF in Microsoft Word

If the PDF is a form, you can sometimes open it directly in Word. Go to File > Open and select the PDF. Word will convert it to an editable document. Click where you want to sign, then go to Insert > Signature Line. Word will create a blank line for your signature.

Print the document, sign it by hand, scan it back in, and save it. Alternatively, if you have a touchscreen or stylus, you can sign directly on the screen using the signature line tool. Like Adobe Reader, this creates a visible signature but not a legally binding one.

Word's signature feature works best for forms that were designed to be printed and signed by hand. If you are working with a PDF that is not form-based, Adobe Reader is usually simpler.

Creating a legally binding signature with a certificate

If you need a signature that holds legal weight — for contracts, loan applications, or documents filed with courts or government agencies — you need a digital certificate. This is a file that proves your identity and is issued by a trusted third party. The signature is encrypted and locked to you, so it cannot be forged or altered.

Services that issue certificates and let you sign PDFs include DocuSign, Adobe Sign, HelloSign, and Notarize. You will need to verify your identity (usually by uploading a photo ID and sometimes a video call), and then you can sign documents. The service encrypts your signature and often sends a copy to the other party automatically. Most charge between $10 and $50 per month, or $1 to $5 per signature if you sign infrequently.

If you are signing a contract with another person or business, ask them which service they use or prefer. Many companies have accounts with one service and can send you a signing link, which is faster than uploading the document yourself.

Signing on a phone or tablet

Most PDF apps on phones and tablets have a built-in signature tool. Open the PDF in Adobe Reader, Google Drive, or your phone's native PDF app. Look for a pen or signature icon, tap it, and draw your signature on the screen with your finger or stylus. You can also take a photo of your handwritten signature and insert it, or type your name in a signature font.

If you use DocuSign or Adobe Sign on a phone, the process is the same as on a computer — you sign the document and it is encrypted and stored. The main difference is that drawing with your finger is usually less precise than using a mouse, so your signature may look less polished. For informal documents, this does not matter. For contracts or official paperwork, consider signing on a computer if possible.

Some phones let you sign using your Apple Pencil or Samsung S Pen, which gives you more control. If you have a stylus, use it instead of your finger for a cleaner signature.

What happens after you sign

Once you sign a PDF, the signature is embedded in the file. If you used a straightforward signature tool (Adobe Reader, Word, or your phone), the signature is just a visual mark — anyone can open the file and see it, but they cannot verify that you actually signed it. If you used a certificate-based service, the signature is encrypted and timestamped, and the recipient can verify it came from you.

In either case, you cannot remove or alter the signature without breaking the document. If you need to make changes after signing, you will have to unsign the document (if the tool allows it), make the changes, and sign again. For this reason, always review the document carefully before you sign.

Save a copy of the signed PDF for your records. If you signed using a service like DocuSign, the company usually stores a copy for you as well. If you signed using Adobe Reader or your phone, the file is only saved where you saved it, so back it up if it is important.

Choosing between straightforward and certified signatures

Use a straightforward signature (Adobe Reader, Word, or your phone) if the document is internal, informal, or just needs to show you reviewed it. Examples include feedback on a draft, approval of a project plan, or a personal agreement between friends.

Use a certified signature (DocuSign, Adobe Sign, or similar) if the document is a contract, a legal agreement, a loan process, or anything that might end up in court. The extra cost and time are worth it because a certified signature proves you signed it and cannot be disputed. If you are not sure which you need, ask the person or organization requesting the signature — they will tell you.

Frequently Asked Questions

Can someone forge a signature I made in Adobe Reader?

Yes. A signature made in Adobe Reader is just a visual mark, not encrypted or tied to your identity. Anyone with the file can copy the signature and paste it on another document. For this reason, do not use straightforward signatures on anything legally important. Use a certified signature service if the document could be disputed or used in court.

What if I sign a PDF and then realize I made a mistake?

If you signed using Adobe Reader or your phone, you can usually undo the signature by opening the file again and deleting the signature mark, then saving. If you signed using a certified service like DocuSign, contact the service — they may be able to void the signature, but it depends on their policy. Always review the document before you sign to avoid this problem.

Do I need special software to sign a PDF?

No. Adobe Reader is free and works on Windows, Mac, and Linux. Most phones and tablets have a built-in PDF app that can sign. If you need a certified signature, you will need to use a service like DocuSign or Adobe Sign, but they work in your web browser — no software to read.

Can I sign a PDF on my phone and send it to someone right away?

Yes. After you sign on your phone, save the file and email it, text it, or upload it to a cloud service like Google Drive or Dropbox. The recipient will see your signature when they open the file. If you used a certified service, they may have a built-in option to send the signed document automatically.

What is the difference between signing and initialing a document?

A signature is your full name or mark, usually at the end of a document to show you agree to the whole thing. Initials are your first and last initials, usually placed next to a specific section or change to show you reviewed just that part. Both can be added using the same tools — just draw or type initials instead of your full signature.