How to add digital signatures to PDF documents

Digital signatures are the most secure document approval option available to companies. Some countries, like the United States, require digital signatures in certain circumstances. In other situations, they’re essential for guaranteeing non-repudiation and eliminating the possibility of tampering.

Important business documents like contracts, proposals, invoices, and others are most commonly shared as PDFs. In this post, you’ll learn everything you need to know. We’ll cover definitions, explain technical infrastructure, and give you a step-by-step guide for securely approving those crucial documents.

Do you need a digital signature or an electronic signature?

People often confuse digital signatures with electronic signatures. While there are a few similarities, they’re more different than they are alike. And understanding what separates the two is essential for determining which one is appropriate for a particular document.

What is an electronic signature?

An electronic signature is any digital mark that is included in a document. If you receive a contract in Microsoft Word and upload a photograph of your handwritten signature (or a generic image file with some scribbled text), then you’ve electronically signed it. Even though they’re not as secure as their digital counterparts, electronic signatures are still fully legally binding.

Some electronic signatures are more secure than others. A tool like PandaDoc, for example, automatically generates a certificate (with the date and time) whenever a document is signed, which makes it more difficult for the signer to refute their approval later on.

What is a digital signature?

A digital signature, on the other hand, is a highly-secure form of approval that relies on technology like secure keys, encryption, and hashing algorithms. If that sounds like a mouthful, don’t worry. The basic concept is relatively straightforward. In short, digital signature software creates a unique copy of the document that is linked to you. This makes it virtually impossible for anybody to change a contract or deny that they signed it. Digital signatures rely on a public key infrastructure (PKI) to enable creation and verification.

You will likely need digital signature capabilities in your company if you negotiate high-level deals, submit certain types of documents to the government (especially in the United States), or work in an industry where there is a significant risk of customers reneging on contracts.

How do digital signatures work?

Let’s explore how digital signatures work with a practical example. Say that Sally sells Bill a car. She sends a sale contract over to Bill, who signs it using his personal key (also called a digital certificate), which he purchased from a certificate authority. Along with his own private key, Bill also has a public key which Sally can use to decrypt (but not encrypt) Bill’s digital signature.

He logs into his document management app, opens up the contract, and uploads his digital certificate. Automatically, the app creates a hashed version of the document (essentially a long garbled string of letters and numbers) using an algorithm. This is called a digest. The software then uses Bill’s personal key to encrypt the hash. The encrypted digest is the digital signature.

Bill sends the document, to which the digital signature is attached, back to Sally along with the public key. She creates a new hash with the same algorithm and uses the public key to decrypt the digest created by Bill. If both digests match, then she knows the contract has not been changed and it was Bill who signed. If they don’t, she knows either the document has been tampered with or Bill didn’t sign it.

How to add a digital signature to a PDF document

You’ll need to follow some general steps before you can sign documents digitally.

First, you’ll need a digital certificate, either from a registered provider or through a self-sign service like Adobe Sign. You cannot add a digital signature to a PDF file without a certificate.

You’ll also need access to an app that allows you to add digital signatures to your documents. Simple tools like Windows Microsoft Word or Adobe Reader can achieve this. Alternatively, you might want to opt for a more feature-rich solution that offers advanced document management capabilities.

It’s usually possible to configure the software, such as by setting a visual signature to display at the bottom of a document whenever you sign (along with your digital signature), so you should familiarize yourself with all the options and set your preferences.

How to add a digital signature to a PDF document with Adobe Acrobat

Adobe Acrobat is one of the most popular apps for adding digital signatures to PDF documents. Follow the steps below to add a signature:

1. Open your document in Adobe Acrobat.
2. Click the Tools tab and scroll down to the Forms and Certificates section. Select Open from the Certificates dropdown menu.
3. Click on Digitally Sign from the new options bar.
4. Select the digital signature you want to use and click Continue. If you have not yet added a digital signature certificate to Adobe Acrobat, select Configure New Digital ID and follow the on-screen prompts.
5. Configure the appearance of the signature and select Sign.

How to add a digital signature to a PDF document with PandaDoc

If you’re using PandaDoc, here’s how to add digital signatures to your documents:

1. Log in to your PandaDoc account. Upload a new PDF by selecting New Document > Upload or select an existing file from the Documents tab on the right of the screen.
2. Open the Content > Fields tab. Drag the Signature field to the relevant place in the PDF.
3. Double click on your new field and follow the on-screen prompts to add your signature.

Why not opt for a dedicated solution?

Adding digital signatures to PDFs is much easier with a dedicated app. A solution like PandaDoc allows you to upload, store, and track all of your PDF documents from one secure dashboard. Adding signatures to PDFs takes only a few clicks, and all recipient signatures and signed documents are stored safely on our secure servers.

You can take advantage of a free trial on any of our premium packages. We also have a forever-free electronic signature plan, the only solution in the industry to offer unlimited document uploads and e-signatures with no strings attached.