Struggling to digitally sign a PDF? Keep reading to learn everything you need to secure your documents.

Digital signatures use advanced software and algorithms to add an extra layer of protection to your PDFs.

This makes them mandatory in certain fields like law, banking, or government, and in some countries, it's required by law.

But before you can digitally sign a PDF, you'll need a digital certificate which acts as a digital form of identification.

If this sounds confusing, then you're not alone.

That's why we've created this guide to give you all the tools and information you need to secure your PDFs with a digital signature.

Key Info

• To digitally sign a PDF, you'll need to have a digital certificate.
• Make sure you have a digital certificate from a reputable Certificate Authority
• Confirm that the certificate you use isn't expired, and remains valid for the required amount of time.
• Use a PDF editor to digitally sign your PDF file, with a signature and your certificate.
• Keep your private keys secure. Don't share them with others, and only install them on secure devices.

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What is a Digital Signature?

The terms "digital signature" and "electronic signature (e-signature)" are often used interchangeably, but they're actually different things.

E-signing refers to writing your signature on a document like you would sign a paper document. Typing, drawing, and pasting an image of your signature are the most common ways to e-sign a PDF.

The drawback to e-signatures is that anyone with a copy of your signature could sign documents like you; there's no way to verify that the correct person signed.

Digital signatures, on the other hand, use digital certificates, special software and algorithms to verify the identity of the sender, so the receiver can trust that the signature is authentic.

Because of these additional layers of security, digital signatures are more secure than electronic signatures.

How Do Digital Signatures Work?

Digital signatures act like a unique fingerprint for the document being signed.

Each time a document is signed, even by the same person, a new, unique, digital signature is generated based on the content of the document, and when it was signed.

This ensures that each digital signature is unique and verifiable.

Digital signatures use Public Key Infrastructure (PKI), which involves a series of steps, hardware, and software designed to securely send information.

PKI works by creating two unique keys:

1. A public key, which everyone can see.
2. A private key, which only the owner should see.

These two keys are used together to verify the authenticity of the signer.

When you digitally sign a document, the signature and a digital certificate (containing the public key) are embedded in it.

The public key corresponds to a private key that is unique to the signer.

Anyone who receives the document can use the public key from the digital certificate to verify the authenticity of the document and the signature.

If the document has been altered after it was signed or if the signature can't be verified, the signature is deemed invalid.

The Entire Digital Signature Process:

1. Creating the Digital Signature: You generate a digital signature using your private key, which is securely stored and only known to you.
2. Verifying the Signature: The receiver of the PDF uses your public key, accessible through your digital certificate (which is embedded in the PDF), to confirm the validity of the signature.

But, before you can digitally sign a PDF, you'll need to obtain a digital certificate.

What Are Digital Certificates?

Digital certificates are like digital ID cards that prove your identity online.

They include your public key (a part of online security) and personal details like your name or email address.

Where Do You Get Digital Certificates?

Trusted organizations called Certificate Authorities (CAs) issue digital certificates, similar to how notaries validate documents. Common CAs include DigiCert, GlobalSign, and GoDaddy.

How to Use Digital Certificates to Sign a PDF

1. Obtain a Digital Certificate: Either your organization will supply you with one to use, or you'll need to purchase one. Regardless, ensure that the digital certificate is from a trusted Certificate Authority.
2. Install the Digital Certificate to your computer: Once you have a digital certificate, you’ll need to install it on your computer. This process can vary depending on the operating system you're using. For Windows, you'll need to download the Certificate and follow the installation Wizard.
3. Digitally sign the PDF with a PDF editor: Use a PDF editor that supports digital signatures to digitally sign the PDF. Follow the prompts and select your certificate. The software will use your private key to create the digital signature and attach your digital certificate to the PDF.

Digital Signature Best Practices

• Trust: Only accept and use certificates from reputable Certificate Authorities.
• Keep Your Private Key Secure: The security of digital signatures depends on your private key being kept private. Be sure not to share your private key with others, or store it on an insecure computer.
• Validity Periods: Digital certificates don't last forever; they come with an expiration date. Confirm that your digital certificate is valid at the time of signing and will remain valid for the duration it needs to be recognized.

Benefits of Digitally Signing a PDF

Digital certificates give the receiver of the document confidence that the document and signature are valid.

Common benefits of digitally signing PDFs include:

Improved Security

Digital signatures use advanced methods to verify who signed the document, when they signed it, and whether the file has been modified.

This enhances trust and validity in the document, and allows the receiver to easily verify the document.

Legal compliance

Digital certificate signatures are mandatory in specific industries and countries, depending on the type of document or transaction.

They're commonly required in industries like legal, healthcare, financial services, and government transactions to enhance security and comply with privacy standards.

For example, in the European Union, digital certificate signatures may be legally required to meet eIDAS standards.

Convenience

Digital certificates are reusable. You do not need a new digital certificate each time you want to digitally sign something. Once you have a digital certificate, you can use it to sign multiple documents until the certificate expires or is revoked.

Traceable

Digital certificates are traceable. They can be traced back to the issuing Certificate Authority (CA) and to the individual or organization to whom they were issued.

Cost-saving

Digital certificates can significantly reduce costs by minimizing the need for physical documents and streamlining identity verification and security processes.

While the initial setup and maintenance may incur costs, the ability to reuse certificates for multiple transactions and the enhanced security they provide generally result in overall cost savings for organizations that need them.

Time-saving

Digital certificates make it faster to verify identities, sign documents, and keep communications secure. This reduces the need for manually checking and verifying paper documents.

This not only speeds up transactions and daily tasks but also cuts down on routine administrative work, saving time and thus money.

Environmentally friendly

Digital certificate signatures are environmentally friendly because they cut down on paper use and reduce the need for transporting documents, which lowers emissions.

When Should I Use a Digital Signature?

Use a digital signature when you're legally required to or when you want to add extra security to your documents.

Remember that obtaining a digital certificate can incur additional costs, and the recipient might need a PDF editor that can validate digital signatures to fully benefit from it.

For less critical situations where additional security isn't necessary, a regular electronic signature (e-signature) will suffice. E-signatures are perfect for signing forms, invoices, and doctor's notes.

How to Digitally Sign a PDF with a PDF Editor

Before you begin digitally signing a PDF, make sure you install a valid digital certificate from a trusted Certificate Authority.

PDF Pro

You'll need a PDF editor that can digitally sign documents.

For Windows users, we recommend PDF Pro, our all-in-one PDF editor, converter, OCR, and security tool.

PDF Pro makes it easy to digitally sign PDFs, add passwords to PDFs, convert files, and more.

Try PDF Pro for free today

To digitally sign your PDF with a visible signature:

1. Open the document you need to sign in PDF Pro. 
2. Press the Secure tab > Sign PDF button.
3. Select your signature, or create one by following the prompts.
4. Once you've selected your signature, click the area of your PDF document that you'd like to add it too. Then press the green checkmark to make it permanent.
5. Then Press Secure tab > Digital Sign.
6. Click on the visible signature that you just added.
7. Click the Manage button in the "Sign document" dialog box.
8. Press Add in the "Digital Certificates" dialog box, and follow the prompts on your screen to install your digital certificate.
9. Press Sign, then choose a Location and Name for your newly signed PDF document.
10. Press Save to finish creating your digitally signed PDF.

To digitally sign your PDF without any visible signatures:

1. Open the document you need to sign in PDF Pro. 
2. Press the Secure tab > Certify Document.
3. Click the Manage button in the "Sign document" dialog box.
4. Press Add in the "Digital Certificates" dialog box, and follow the prompts on your screen to install your digital certificate.
5. Press Sign, then choose a Location and Name for your newly signed PDF document.
6. Press Save to finish creating your digitally signed PDF.

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How to Digitally Sign a PDF with Adobe Acrobat DC

Adobe Acrobat DC is a powerful PDF editor for both Windows and Mac users.

While Acrobat is also known for its steep price tag and high learning curve, its powerful and modern tools are great for those who need the highest levels of security for their documents.

1. Open your PDF in Adobe Acrobat, then go to All Tools > more > Use a certificate.
2. Alternatively, from the Acrobat Home screen, select See all tools > Use a certificate (under the Protect section) > choose the file you wish to certify.
3. The Use a certificate tool will appear in the left pane.
4. For a visible digital signature, select Certify (visible signatures), then use the Drag New Signature Rectangle in the dialog box that appears.
5. For an invisible signature, choose Certify (invisible signatures).
6. Confirm your action in the Save as Certified Document dialog box.
7. If using a visible signature, use the mouse to draw a rectangle where you want your signature to appear.
8. In the Sign with a Digital ID dialog, select your Digital ID or configure a new one, then click Continue.
9. Review the document by selecting Review, then sign it by clicking Sign.
10. Save the certified PDF when prompted. Your document is now certified.

Secure Your PDFs With a Digital Signature

Digital signatures use advanced software and algorithms to add an extra layer of security and trust to PDFs.

Once you have a digital certificate from a Certificate Authority, you'll need to use a PDF editor to digitally sign your PDF.

For Windows users, we recommend PDF Pro, our all-in-one PDF editor, converter, security tool, and more.

PDF Pro makes it easy to protect and secure PDF documents, sign PDFs, and recognize text in PDFs.

Other things PDF Pro can help you with:

• How to password protect a PDF
• How to combine password protected PDFs
• How to redact a PDF
• How to make a fillable PDF

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FAQ

How do I digitally sign a PDF document?

You'll need a digital certificate from a trusted Certificate Authority.

Then you'll need to use a PDF editor like PDF Pro to digitally sign your PDF by using your digital certificate.

How to add a digital signature in PDF for free?

While there may be online tools that can help you create your own digital certificate and digitally sign PDFs, official or legal documents will likely require that the digital certificate is from a reputable Certificate Authority like DigiCert, GlobalSign, and GoDaddy.

How do I create a digital signature?

Once you have a digital certificate, use a PDF editor like PDF Pro to digitally sign your PDF. Steps: Open your PDF in PDF Pro > Secure tab > Certify Document > Manage button in the "Sign document" dialog box > Add in the "Digital Certificates" dialog box > follow the prompts on your screen to install your digital certificate > Sign > choose a Location and Name for your PDF > Save.

How to digitally sign a PDF without Adobe?

Use an affordable Adobe alternative like PDF Pro. Try PDF Pro for free today

Once you have a digital certificate, use a PDF editor like PDF Pro to digitally sign your PDF. Steps: Open your PDF in PDF Pro > Secure tab > Certify Document > Manage button in the "Sign document" dialog box > Add in the "Digital Certificates" dialog box > follow the prompts on your screen to install your digital certificate > Sign > choose a Location and Name for your PDF > Save.