What a digital signature actually is and why you need one
A digital signature is a way to sign documents electronically that proves you created or approved them. It is not the same as typing your name or scanning a handwritten signature — a real digital signature uses encryption to attach your identity to a specific document, and it cannot be copied to a different file.
When you digitally sign a document, the software creates a unique code based on the document's contents and your private key (a secret number only you have). If someone changes even one word in the document after you sign it, the signature becomes invalid. This makes digital signatures useful for contracts, tax forms, loan applications, and any document where you need proof that you approved it on a specific date.
The method you use depends on what you are signing and who needs to verify it. A simple electronic signature (like clicking "I agree" on a website) works for many everyday situations. A certified digital signature, which uses a certificate from a trusted authority, is required for legal documents in some states and for certain government filings.
Key Takeaways
- A digital signature uses encryption to prove you signed a specific document and that it has not been changed since you signed it.
- Simple electronic signatures (typing your name or clicking "I agree") work for most everyday documents, while certified digital signatures are needed for legal contracts and government filings in some situations.
- To create a certified digital signature, you need a digital certificate from a certificate authority, which you can obtain through your bank, a third-party provider, or your employer.
- Most document software (Adobe, Microsoft Word, Google Docs) has built-in tools to add digital signatures without needing separate software.
- The person receiving your signed document needs compatible software to verify your signature, so check with them before signing.
The difference between electronic signatures and certified digital signatures
An electronic signature is the broad category — it includes anything from typing your name in a document to clicking a checkbox that says "I agree." It proves you intended to sign something, but it does not use encryption and does not prove the document has not been changed. Electronic signatures are legal for most contracts in the United States under the E-SIGN Act, but they are not accepted for wills, powers of attorney, or certain real estate transactions.
A certified digital signature (also called a may have access to digital signature) uses a digital certificate issued by a trusted authority. It includes encryption, a timestamp, and proof of your identity. Certified signatures are required for legal documents in some states, for filing taxes electronically with the IRS, and for signing documents in some industries like healthcare or finance. They carry more legal weight because they are harder to forge or deny.
For most everyday use — signing a PDF you received from a friend, approving a document at work, or signing a contract with a small business — an electronic signature is sufficient. You only need a certified digital signature if the document is legally binding, if a government agency requires it, or if the other party specifically asks for one.
How to get a digital certificate
If you need a certified digital signature, you first need a digital certificate — a file that contains your identity information and a private key that only you have. You obtain this from a certificate authority, an organization trusted by the government or industry to verify identities.
The easiest route is often through your bank. Many banks issue digital certificates to customers for free or a small fee. Contact your bank's business or online services department and ask if they offer digital certificates. They will verify your identity (usually in person or through video call) and issue you a certificate file that you download to your computer.
If your bank does not offer certificates, you can get one from a third-party certificate authority. Common providers include DigiCert, Sectigo, and GlobalSign. You will pay a fee (typically $50 to $200 per year) and go through an identity verification process. Some employers also issue digital certificates to employees for signing work documents — ask your IT department if this is available to you.
Once you have a certificate, it is stored on your computer (or on a USB token for extra security). You will need to remember the password you set when you created it, because you will enter it each time you sign a document.
How to add a digital signature in Adobe Acrobat and PDF readers
Adobe Acrobat is the most common tool for signing PDFs. Open the document you want to sign, click the "Sign" button in the toolbar, and select "Add Signature." You will see three options: type your signature (just your name), draw your signature (using your mouse or trackpad), or use an image of your handwritten signature.
If you have a digital certificate, click "Add Digital Signature" instead. You will be asked to select your certificate file and enter the password you created when you got the certificate. Adobe will then encrypt your signature into the PDF. The document will show when it was signed and by whom, and anyone who opens it can verify that the signature is valid and the document has not been changed.
If you do not have Adobe Acrobat (the paid version), you can still sign PDFs with free tools. Preview on Mac has a built-in signature tool — open the PDF, click the Markup button, and select "Signature." On Windows, Microsoft Edge has a basic signing feature. Google Docs and Microsoft Word also allow you to insert a signature image, though these are not encrypted digital signatures.
How to add a digital signature in Microsoft Word and Google Docs
In Microsoft Word, open the document and go to Insert > Signature Line. This creates a space where you or someone else can sign. When it is time to sign, double-click the signature line and you will be prompted to type your name or select a signature image. This is an electronic signature, not a certified digital signature, but it is useful for documents you are sharing within your organization.
If you have a digital certificate, you can add a certified signature in Word by going to File > Info > Protect Document > Add a Digital Signature. Select your certificate, enter your password, and Word will encrypt your signature into the document. Anyone opening the document will see that it is signed and can verify the signature is valid.
Google Docs does not have a built-in digital signature tool, but you can insert an image of your signature. Go to Insert > Image and upload a photo or drawing of your handwritten signature. This is not a certified digital signature — it is just a visual representation — but it works for informal documents. For legally binding documents in Google Docs, you will need to download the file as a PDF and sign it in Adobe or another PDF tool.
What happens after you sign a document digitally
Once you sign a document with a certified digital signature, the document is locked. If anyone tries to change even a single word, the signature will show as invalid. The person receiving the document can open it and verify that your signature is real, that it has not been tampered with, and when you signed it.
The recipient does not need a digital certificate to verify your signature — they just need compatible software (Adobe Reader is free and works for this). They can see your name, the date and time you signed, and whether the document has been altered since you signed it.
Keep a copy of the signed document for your records. If you signed a contract or important agreement, store it somewhere you can find it later. If you signed a tax form or government document, follow the instructions for where to send it — some agencies want the original file, while others accept copies.
Common problems and what to do about them
The most common issue is that the recipient cannot verify your signature. This usually happens because they do not have the right software or because your certificate came from an authority their software does not recognize. Before you sign an important document, ask the recipient what software they use and whether they can verify signatures from your certificate authority. If there is a mismatch, you may need to use a different method or get a certificate from a more widely recognized authority.
Another issue is forgetting your certificate password. If this happens, you will not be able to sign documents with that certificate. You will need to contact your certificate authority or bank to reset it, or you may need to request a new certificate. This is why it is important to store your password somewhere secure (like a password manager) when you first create your certificate.
If you are signing a document that will be filed with a government agency, check their website first to see what type of signature they accept. Some agencies only accept certified digital signatures from specific certificate authorities. Filing with the wrong type of signature can delay your document or cause it to be rejected.
Frequently Asked Questions
Can I use a digital signature on a will or power of attorney?
It depends on your state. Some states accept digital signatures on wills and powers of attorney, while others require a handwritten signature and witness signatures. Check your state's laws or consult an attorney before signing these documents digitally. For legal documents, a certified digital signature is safer than an electronic signature because it is harder to dispute.
Is a digital signature the same as a scanned handwritten signature?
No. A scanned signature is just an image — anyone can copy it to another document. A digital signature uses encryption to tie your identity to a specific document. If the document changes, the digital signature becomes invalid. For important documents, always use a real digital signature, not a scanned image.
Do I need a digital certificate to sign documents at work?
Not always. Many workplaces use simple electronic signatures (like typing your name or clicking "I agree") for internal documents. Ask your IT department or manager whether your company issues digital certificates or whether electronic signatures are sufficient for the documents you sign.
What if someone signs a document with my digital certificate without my permission?
This is why your certificate password is important — if someone has your password, they can sign documents as you. Keep your password secure and never share it. If you think someone has used your certificate without permission, contact your certificate authority immediately to revoke it and request a new one.
Can I sign a document on my phone or tablet?
Yes, but it depends on the app. Adobe Acrobat Reader on iOS and Android allows you to add electronic signatures (typing or drawing your name). For certified digital signatures, you will need an app that supports your certificate, which is less common on mobile devices. For important documents, signing on a computer is usually more reliable.