How do digital signatures work?

Gain a better understanding of digital signatures and find out how they make electronic forms and agreements valid.

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Over 1 million satisfied users.

With an average of 4.6 and 4.9-star ratings on Google Play and Apple App Stores, Fill is the best digital signature app for mobile and desktop. Don’t just take our word for it. You decide.

electronic signature software for business

What is Fill?

Fill is a cloud-based solution that lets you use digital signatures to ensure the security and integrity of documents at every stage of the signing process. It provides a platform for approving, sharing, and encrypting important documents.

How digital signature works

Every time you sign a document, the app creates a unique string of characters called an encrypted hash. This serves as your digital signature. When shared, it protects your signed document from tampering during transit. Any attempt to alter its content will change the hash, so your receiver will see right away if your digital signature is still valid or not.

a diagram on how digital signatures work

Maintain document integrity while simplifying your workflow

Gain a competitive edge by protecting documents with the highest level of encryption. With Fill, you have everything you need to safeguard your esignature transactions without wasting time and effort. It’s a fast and cost-efficient way to keep your forms and agreements safe from data theft, unauthorized access, and tampering.

Fill feature signer authentication and verification

Validates the authenticity of the signed document

Go through transactions knowing that each digitally signed contract comes from a verified source. Build trust and loyalty by providing a secure and effective way to determine whether a document is genuine or fake.

Provides proof of document transmission

Each digitally signed document has a detailed audit log, complete with timestamps and records of transmission. This lets you prove the validity of electronic signatures in online agreements.

Fill provides audit trail so you can track your documents
Making sure all information are safe and secured

Ensures the accuracy and consistency of information

Prevent unauthorized changes to your digitally signed documents while complying with local and international data privacy regulations. You also reduce legal risks by eliminating typographical errors.

Digital signature software key features

Remote document signing

Digitally sign forms and contracts using your tablet or cell phone. Never miss another opportunity to close an important deal with the help of our flexible document signing solution.


Signer identity verification

Safeguard high-level transactions by asking signers to prove their identity before adding a digital signature. Quickly run a verification check to avoid fraud and forgery.


Real-time audit trails and logs

Monitor the changes in your digitally signed forms as they happen. Detailed audit logs let you track any unusual activity that could invalidate your digital signature.


Hassle-free app integrations

Connect Fill with third-party apps so you can add digital signatures without switching between platforms. Use Fill on Zapier to streamline your document workflows.


256-bit encryption

Feel confident knowing that your documents are protected by the highest level of end-to-end encryption. Keep sensitive files safe against any unauthorized access.


What our users say about us

“Easy way to get documents signed electronically. Fill saves a lot of time getting to appointments in person when signing can be done via mobile.”

Tim Crump, Cioa

a mobile phone using Fill digital signature app to create contract

Secure digital signatures for online documents

Digitally sign documents on your phone, tablet, laptop, and desktop without the hassle. Start using the Fill app today.

Know more about how Fill’s digital signatures work

Digital signatures work by validating a document’s integrity. Although considered a form of e-signature, a digital signature offers more security as it uses advanced encryption to keep a signed agreement from being modified or altered. Advanced level encryption also makes it virtually impossible for others to snoop on your private information. With it, you can share documents securely and not worry about potentially losing your data to identity thieves and online scammers.

Digital signatures also work in a way that only those with access to the sender’s public key can decipher the contents of the document or message. It serves as a safety seal that helps ensure the legitimacy of each negotiation. It also helps verify the signer’s identity, making it easier to determine whether a particular transaction is fake or genuine.

Nowadays, online document signing services like Fill use digital signatures to validate contracts. Since a digitally signed document bears a unique hash code, it’s easier to tell whether its contents have been replaced or forged. Any changes made will completely change the hash, which leads to your contract becoming invalid and unenforceable. You can also use digital signatures to track the changes made to your documents via timestamps and audit trails.

Digital signatures are as legally binding as their handwritten counterparts. There are also laws honoring the use of digital signatures online. In the United States, a federal law known as the E-Sign Act (Electronic Signatures in Global and National Commerce Act) has laid out specific rules to honor the validity of digital signatures in electronic documents.

Based on the E-Sign Act, a digital signature is only considered legally binding if it meets the four basic requirements. First off, all signers must display a clear sign of consent to use digital signatures for online document signing. Second, signers must agree to e-sign documents while implying their intent to conduct business transactions via electronic means. Third, the contract management software used should have what it takes to provide a clear and detailed signature attribution. There should be a way to validate the signer’s identity by looking at the audit trail. The same rule applies when using an online document signing app like Fill.

Lastly, there should be a way to maintain records that accurately reflect the information covered in each contract or agreement. Most e-sign document services do this by allowing signers to obtain a fully signed copy of the electronic contract or form. With Fill, you can easily do this by downloading a signed copy of your document via email.

Creating a digital signature doesn’t require a lot of steps. With the help of a reliable e-sign document app or software, you can create a digital signature either by typing or drawing. You can even transform your handwritten signature into a digital signature without printing or scanning.

To create a digital signature using Fill, you can open its mobile app or go to your web dashboard. Once logged in, you simply upload a new document or complete an existing signature request. Tap on the Insert Signature icon located at the top menu. You may then choose to type, draw, or upload a handwritten copy of your signature. Drag and resize your signature as you see fit. It’s that simple.

With Fill, you can simplify your digital signature creation process even further. It’s like having your own personal assistant guide you as you sign and fill out forms. You’ll know exactly where to type and which areas to sign, freeing you from any possible cause of delays or confusion. On top of this, our mobile and web app also uses document automation to speed up the way you fill out forms. Using your previously typed entries, you can automatically populate fields and submit your forms while avoiding typos and mismatched information.

Fill supports multiple documents and image formats. Currently, it supports PDFs, DOCX, PNG, and JPG files. You can also create templates using your existing documents and share them as forms. That’s not all. Our mobile and web app also has built-in tools for editing and annotating PDFs. You also have an option to combine multiple documents in a single signature request.

On top of this, our online app also functions as a PDF filler, making it easier for you to fill out online forms quickly. With Fill, you can also convert your Word documents automatically and download them as PDFs. There’s no need to convert each file or document manually, giving you more time to focus on urgent tasks such as closing deals and improving your work productivity.

The best thing about Fill is that it’s so simple and easy to use. Even if your signers don’t have an existing account, you can still send a signature request and have them sign your form or agreement directly via link or email. You can also send signature requests securely via online fax. We also make it easy for you to access and view your real-time analytics for online forms, which will come in handy when conducting surveys and running event polls.

Yes, it’s safe to use Fill eSignature to sign documents online, including forms and PDFs. You can also use our online tool in any web or mobile browser. Installing the Fill app for mobile and desktop is optional but strongly recommended.

Here at Fill, we are committed to keeping your data safe. With 256-bit encryption, we can assure the safety of all your online document transactions. Our online document signing tool also meets the requirements of HIPAA, GLBA, and other privacy regulations. You can use our eSignature tool to execute legal documents such as deeds and contracts. Our GDPR-compliant platform is also secure enough to handle all your legal paperwork.

With Fill, you can securely sign your documents online while keeping track of its activity via instant email alerts and audit logs. Use our online eSignature tool to sign agreements and fill out forms using only your laptop or cell phone. Instead of in-person meetings, you can also choose to sign your documents remotely. This way, you can save on travel expenses while having the freedom to execute any document regardless of time or location. You can also avoid the risk of losing your documents while in transit, especially if you’re mailing them through your local courier service.