What an electronic signature does and where it works

An electronic signature is a digital mark you place on a PDF to show you have reviewed and agreed to a document. It is not the same as your handwritten signature scanned into an image — it is a cryptographic record that proves you signed the document at a specific time, and that the document has not been altered since you signed it.

Electronic signatures work in most business and legal contexts. Banks, insurance companies, employers, and government agencies accept them for contracts, loan applications, tax forms, and employment paperwork. Some documents — like wills, powers of attorney, and real estate deeds — have specific legal requirements that vary by state, so you should check your state's laws before signing those types of documents electronically.

The signature itself appears as a visual mark on the PDF, but the real work happens behind the scenes. When you sign, the software creates a digital certificate that is tied to that specific document. If someone changes even one word after you sign, the signature becomes invalid and the change is visible to anyone who checks.

Key Takeaways

  • Most PDF tools let you draw, type, or upload an image of your signature, and all three methods create a valid electronic signature for business documents.
  • You do not need special software or a digital certificate to sign most PDFs — built-in tools in Adobe Reader, Preview on Mac, and free online tools work for everyday documents.
  • Legally binding signatures that prove your identity require a digital certificate from a trusted provider, which costs money and takes time to set up.
  • Once you create a signature, you can save it and reuse it on future documents without redrawing or retyping it each time.

Signing with Adobe Reader or Acrobat

If you have the PDF open in Adobe Reader (the free version), look for the "Sign" button in the toolbar on the right side of the screen. Click it, then choose "Add Signature." You will see three options: draw your signature with your mouse or trackpad, type your name in a signature font, or upload an image of your handwritten signature.

Draw works best if you have a stylus or trackpad you can control precisely. Type is faster and looks cleaner if you prefer a printed name. Upload lets you use a photo of your actual signature — write your name on paper, photograph or scan it, and upload the image file.

After you choose your method, click where on the PDF you want the signature to appear. The signature will be placed at that spot. You can resize it by dragging the corners. Once you are satisfied, click "explore" and then save the document. Adobe Reader will save it as a new file so your original stays unsigned.

If you have Adobe Acrobat Pro (the paid version), you get additional options: you can set up a saved signature so you do not have to redraw it every time, and you can send documents to others for them to sign in sequence. For most people signing their own documents, Adobe Reader is enough.

Signing on Mac with Preview

Preview, the built-in PDF viewer on Mac, has a signature tool built in. Open your PDF, then click the Markup toolbar button (it looks like a pen in a circle). Click "Signature," then "Manage Signatures." You will be prompted to create a signature by drawing on your trackpad or taking a photo with your Mac's camera.

Once you have created a signature in Preview, it is saved to your Mac and you can use it on any PDF you open in Preview. Click where you want it to appear, and Preview will place it at that spot. You can resize and move it before you save the document.

Preview signatures are simpler than Adobe's — you cannot add text-based signatures or upload images — but they work for most everyday documents. The signature is embedded in the PDF and will be visible to anyone who opens the file.

Using free online tools

If you do not want to install software, several free websites let you upload a PDF, add a signature, and read the signed version. Smallpdf, ILovePDF, and DocuSign's free tier all offer this. Upload your PDF, click where you want to sign, draw or type your signature, and read the result.

The trade-off with online tools is privacy: your PDF is uploaded to someone else's server. Most reputable services delete files after a few hours, but if your document contains sensitive information, you may prefer to sign locally using Adobe Reader or Preview instead.

Online tools are useful when you need to sign something quickly and do not have PDF software installed, or when you need to send a document to someone else to sign and want a tool that does not require them to install anything either.

Creating a reusable signature you can use repeatedly

If you sign documents regularly, you can save your signature so you do not have to redraw or retype it every time. In Adobe Reader, go to Edit > Preferences > Signatures. Click "New," then create your signature using any of the three methods. Give it a name like "My Signature" and click OK. The next time you sign a document in Adobe Reader, your saved signature will appear as an option.

In Preview on Mac, your signature is automatically saved the first time you create it. You can manage your saved signatures by going to Markup > Signature > Manage Signatures.

For online tools, most do not save signatures between sessions, so you will need to create a new one each time. If you use an online tool frequently, consider switching to Adobe Reader or Preview so you can save your signature and work faster.

The difference between a straightforward signature and a legally binding one

The signatures described above — drawn, typed, or uploaded images — are electronic signatures. They show that you signed the document and prove the document has not been changed since you signed it. For most business purposes, this is enough.

A digital signature is different. It includes a digital certificate that proves your identity. The certificate comes from a trusted third party and confirms that you are who you say you are. Digital signatures are required for some legal documents and are often used in government and finance.

To get a digital certificate, you go through a verification process with a provider like DigiCert, GlobalSign, or Sectigo. They confirm your identity, issue you a certificate, and you install it on your computer. This costs money — typically $100 to $300 per year — and takes a few days to set up. For everyday documents, a straightforward electronic signature is sufficient and free.

Troubleshooting common signature problems

If your signature does not appear where you clicked, the PDF may be locked or in a format that does not support signatures. Try opening it in a different tool — if it works in Adobe Reader but not in Preview, the document itself is fine and the tool just does not support it.

If you cannot find the Sign button in Adobe Reader, make sure you have the latest version installed. Go to Help > Check for Updates. Older versions of Adobe Reader do not have the signature feature.

If you signed a document and then realized you made a mistake, you cannot undo the signature. You will need to open the original unsigned PDF and sign it again. This is why it is a good idea to keep a copy of the unsigned document before you sign.

If someone else needs to sign the document after you, send them the unsigned original, not your signed version. If you send your signed version, they will have to sign on top of your signature, which can look messy. Most PDF tools let you send documents for sequential signing, which handles this automatically.

Frequently Asked Questions

Is an electronic signature legally valid?

Yes, for most documents. The U.S. Electronic Signatures in Global and National Commerce Act (E-SIGN) and the Uniform Electronic Transactions Act (UETA) recognize electronic signatures as legally binding for contracts, agreements, and most business documents. Some documents — like wills and real estate deeds — have specific requirements that vary by state, so check your state's laws for those.

Can someone forge my electronic signature?

A straightforward electronic signature (drawn, typed, or uploaded image) can be copied if someone has access to the file. A digital signature with a certificate is much harder to forge because it is tied to your identity and the specific document. For high-security documents, use a digital certificate.

What if I sign a PDF and then want to change it?

Once you sign a PDF, the signature proves the document has not been altered. If you change anything after signing, the signature becomes invalid. You will need to open the original unsigned version, make your changes, and sign again.

Do I need to buy software to sign PDFs?

No. Adobe Reader is free and includes signature tools. Preview on Mac is free and built in. Several free websites let you sign online. You only need to buy software if you want advanced features like batch signing multiple documents or sending documents to others for sequential signing.

Can I use the same signature on every document?

Yes. Save your signature in Adobe Reader or Preview, and it will be available every time you sign a document. This is faster than redrawing or retyping your signature each time.