Whether it's a rental agreement, an NDA, or an invoice approval, signing a PDF no longer means printing, signing by hand, scanning, and emailing back. You can add a legally valid signature in under a minute — entirely in your browser.
This guide covers three types of PDF signatures, when each makes sense, and how to do all of them free.
The Three Types of PDF Signatures
Understanding which type you need saves time and avoids rejection.
1. Electronic Signature (E-Signature)
A typed name, drawn signature, or uploaded image of your handwriting placed on the PDF. This is what most people mean when they say "sign a PDF." It is legally binding in most countries under laws like the US ESIGN Act and EU eIDAS Regulation for everyday contracts.
2. Digital Signature (Cryptographic)
A cryptographic certificate embedded in the PDF that proves identity and detects any tampering after signing. Required for regulated industries (finance, government, healthcare) and when a certificate authority must validate the signer. Requires a paid certificate from a trust provider.
3. Wet Signature Scan
A scanned image of your physical signature placed as an image overlay. Legally the same as an electronic signature in most jurisdictions — it just looks more "official" to some recipients.
For 95% of use cases, option 1 is what you need. This guide focuses on that.
How to Sign a PDF with PDFlexa (Step by Step)
Reduce your PDF file size instantly. No software needed.
- Go to PDFlexa Sign PDF
- Upload your PDF (click or drag and drop)
- Choose your signature method:
- Type — type your name and choose a handwriting-style font
- Draw — draw your signature with mouse, trackpad, or touchscreen
- Upload — upload a PNG photo of your handwritten signature
- Click Place Signature and drag it to the correct spot on the document
- Optionally add your initials, date, or job title as additional text fields
- Click Download Signed PDF
Your signed PDF downloads instantly. No account required, no watermark.
Adding Multiple Signatures to One PDF
If you need to sign as two parties (or need a second signer's box):
- Sign the document yourself using the steps above
- Download the signed PDF
- Upload it again
- Add the second signature field at a different position
- Download the final version
For formal multi-party signing workflows (where each party signs independently and gets a notification), use a dedicated e-signature service like DocuSign or HelloSign — these maintain an audit trail that some contracts require.
How to Add a Signature Image from Your Handwriting
Turn any PDF into an editable Word document in seconds.
If you want your actual handwriting as the signature (not a font):
- Sign on white paper with a black pen
- Photograph it with your phone or scan it
- Crop tightly around the signature and save as PNG
- In PDFlexa Sign, choose Upload image and select your PNG
Tip: Use a photo editing tool to set the background to transparent before uploading — your signature will sit cleanly on the document without a white rectangle behind it.
How to Sign on Mobile
PDFlexa works on any mobile browser (iOS Safari, Android Chrome):
- Open your browser and go to pdflexa.com
- Navigate to Sign PDF
- Tap Choose a file and select the PDF from Files (iOS) or Downloads (Android)
- Use your finger to draw your signature in the signature panel
- Place it and download
For frequent mobile signing, add PDFlexa to your home screen (Share → Add to Home Screen on iOS, or the three-dot menu → Add to Home Screen on Android) for one-tap access.
Is an Online PDF Signature Legally Binding?
In most countries, yes. Electronic signatures have the same legal weight as handwritten signatures for the vast majority of personal and business documents:
| Jurisdiction | Law | Valid for | |---|---|---| | United States | ESIGN Act (2000) | Most contracts, agreements | | European Union | eIDAS Regulation (2016) | Simple & advanced e-signatures | | United Kingdom | Electronic Communications Act 2000 | Most contracts | | Australia | Electronic Transactions Act 1999 | Most contracts |
Not valid (requires qualified digital signature or wet ink): court filings in some jurisdictions, wills and testaments, certain real estate transactions, and regulated financial instruments. Always check with a lawyer for high-stakes documents.
What to Do if a PDF Has Signature Fields Already
Some PDFs have interactive signature fields pre-placed by the sender. These appear as blank rectangles with a pen icon:
- Open the PDF in PDFlexa Sign
- Click the interactive field — a signature panel appears
- Draw, type, or upload your signature
- Click Apply
- Download
If the PDF requires a certificate-based digital signature (you'll see a blue badge or certificate requirement in the field), you'll need Adobe Acrobat with a digital ID certificate.
Frequently Asked Questions
Can I sign a PDF on my iPhone or Android phone? Yes. PDFlexa runs entirely in the browser and works on all modern mobile browsers. You can draw your signature with your finger or upload a photo of it.
Does the signed PDF look different from a "real" signed document? No. The signed PDF looks identical to one signed in Adobe Acrobat or DocuSign for the recipient. The signature appears as an embedded graphic on the page.
Can the recipient verify my signature is authentic? For basic e-signatures, no cryptographic proof is embedded. If your contract requires verifiable identity proof, use a qualified digital signature service. For most everyday documents — leases, invoices, approvals — a simple e-signature is fully sufficient.
How do I sign only one page of a multi-page PDF? PDFlexa lets you place the signature on any specific page. Upload the full document, place the signature on the target page, and the rest of the pages remain unchanged.
Can I remove a signature after signing? If you have the original unsigned PDF, simply use that instead. There is no "undo" on a downloaded signed PDF without access to the source. To create a clean copy, split the relevant pages from the unsigned original.
Is it safe to upload confidential documents to sign online? PDFlexa processes the file in your browser — for the sign tool specifically, the file is never sent to a server. All rendering and signature embedding happens locally using pdf-lib, a client-side JavaScript library.