How to Add a Digital Signature to a PDF

What a digital signature actually does

A digital signature is a way to sign a PDF document on your computer instead of printing it, signing it by hand, and scanning it back. When you add a digital signature, you are creating a record that you (or someone using your account) opened that specific document and approved it. The signature stays attached to the file and moves with it if someone forwards the PDF to another person.

Digital signatures are not the same as typing your name or drawing a signature with your mouse. A real digital signature uses encryption — a locked code that proves the document has not been changed since you signed it. If someone edits the PDF after you sign, the signature breaks and shows as invalid. This is why banks, courts, and employers often require them instead of handwritten signatures.

Most PDFs you encounter — contracts, forms, tax documents — can accept a digital signature. You do not need special software to add one, though the method depends on what program you are using to open the PDF.

Key Takeaways

Adobe Acrobat Reader (the free version) lets you add a signature by clicking Tools, then Sign, then Add Signature, and either drawing one with your mouse or uploading an image of your handwritten signature.
Microsoft Edge and Google Chrome both have built-in signature tools — open the PDF in your browser, click the pen icon or markup tools, and draw or add your signature directly.
Some PDFs have signature fields already marked by the sender; clicking the field and adding your signature is faster than signing a blank document.
After you sign, save the document with a new filename so you keep both the unsigned and signed versions.
A digital signature proves you opened and approved that exact document, and it becomes invalid if anyone changes the file afterward.

Adding a signature in Adobe Acrobat Reader

Adobe Acrobat Reader is free and installed on most computers. Open your PDF, then look at the top menu bar and click Tools. A sidebar will appear on the right side of your screen. Click Sign, then click Add Signature.

You will see three options: Draw, Type, or Image. Draw lets you use your mouse or trackpad to write your signature directly on the screen — click in the box and drag to create your signature. Type lets you enter your name in a typed font that looks like a signature. Image lets you upload a photo of your handwritten signature if you have one saved on your computer.

Choose whichever method matches what the document requires. Once you have created your signature, click explore. A box will appear on the PDF asking where you want to place the signature. Click and drag to position it, or click once to place it in a pre-marked signature field. After you place it, the signature is added to the document.

Save the file when ready by pressing Ctrl+S (Windows) or Command+S (Mac). Adobe will ask whether you want to save it as a new file or replace the original. Choose Save As and give it a new name so you keep both versions.

Adding a signature in your web browser

If you open a PDF in Microsoft Edge or Google Chrome, you do not need to read anything. Look for a pen icon or markup button — in Edge it is usually in the top right corner, and in Chrome it appears as a pencil icon. Click it to open the drawing tools.

Select the pen or highlighter tool and draw your signature directly on the PDF. The signature appears as a drawn image on top of the document. When you are finished, use your browser's print function (Ctrl+P or Command+P) and select Save as PDF to save the signed version to your computer.

This method is faster for straightforward signatures but does not create the same kind of encrypted, tamper-proof signature that Adobe Acrobat does. It is fine for informal documents, contracts between people you know, or forms you are sending to someone who just needs proof you reviewed it.

Signing PDFs with pre-made signature fields

Many documents sent to you for signature already have boxes marked for where your signature should go. These are called signature fields. When you open the PDF, you will see empty boxes labeled "Sign here" or "Signature".

Click directly on the field. Adobe Acrobat Reader will recognize it and open your signature options (Draw, Type, or Image). Create or select your signature and click explore. The signature will automatically fit into the box. If the document has multiple signature fields — for example, one for you and one for a witness — repeat this step for each field.

Pre-made fields are much faster because you do not have to position your signature manually. The sender designed the form knowing exactly where signatures should appear.

What happens after you sign

Once you save a digitally signed PDF, the signature is locked to that document. If anyone opens it later and tries to edit the text, add pages, or change anything, the signature will show as invalid or broken. This is the security feature that makes digital signatures useful for important documents.

You can send the signed PDF to anyone, and they can open it in any PDF reader. They will see your signature and can verify it has not been tampered with. Some programs (like Adobe Acrobat Pro, which costs money) let you add a timestamp or certificate to make the signature even more official, but the free version is enough for most everyday use.

Keep both the unsigned and signed versions of important documents. The unsigned version is your record of what you were asked to sign, and the signed version is your proof that you did.

Signing PDFs on your phone or tablet

If you need to sign a PDF on an iPhone, iPad, or Android device, the process is similar but slightly different. On an iPhone or iPad, open the PDF in the built-in Books app or Adobe Acrobat Reader app. Look for a pen or markup icon, tap it, and draw your signature with your finger. On Android, Adobe Acrobat Reader has the same Tools menu — tap it, select Sign, and draw your signature.

The signature you create on a phone or tablet is just as valid as one created on a computer. Save the file to your device, then email it to yourself or upload it to cloud storage so you can access it from your computer later.

Common problems and how to fix them

If you click on a signature field and nothing happens, the PDF may be locked or read-only. Try opening it in a different program — Adobe Acrobat Reader usually works when other readers do not. If you are using a browser and the signature does not save, use the print-to-PDF method instead: press Ctrl+P (or Command+P on Mac), select Save as PDF, and save it to your computer.

If your signature looks messy or too small, you can undo it and try again. In Adobe, press Ctrl+Z (or Command+Z on Mac) to undo the last signature, then redraw it. If you are signing in a browser, refresh the page to start over.

Some older PDFs do not support digital signatures at all. If you cannot find a signature option, the document may have been created in an older format. In that case, print it, sign it by hand, and scan it back, or ask the sender to provide a newer version of the form.

Frequently Asked Questions

Is a digital signature legally binding?

Yes, in most places. The U.S. E-SIGN Act and similar laws in other countries recognize digital signatures as legally valid for contracts and official documents. However, some documents — like wills or real estate deeds — may have specific requirements about what kind of signature is acceptable. If you are signing something important, ask the other party whether a digital signature is acceptable before you send it.

Can someone forge my digital signature?

If you use the Draw or Type method, yes — anyone could draw or type your name. The encryption protection only works if you use a certified digital certificate, which costs money and is usually only needed for very official documents. For everyday use, a drawn or typed signature is fine because it shows you opened and approved that specific document, and the signature breaks if anyone edits it afterward.

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

You cannot unsign a document, but you can create a new version. Open the unsigned copy you saved earlier, make the correction, and sign it again. Send the corrected version to the other party and ask them to discard the first one. Always keep the unsigned original so you can do this if needed.

Do I need Adobe Acrobat Pro to sign PDFs?

No. The free Adobe Acrobat Reader has all the tools you need to add a signature. Acrobat Pro (paid) adds features like timestamps and certificates, but those are only necessary for highly find or official documents. For contracts, forms, and most everyday documents, the free version is enough.

Can I use the same signature for every document?

Yes. Once you create a signature in Adobe Acrobat Reader, it saves it and offers it again the next time you sign something. You can also upload an image of your handwritten signature and reuse it. This makes signing multiple documents much faster.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.