How to Add Digital Signatures to PDFs in an Editor App (2026)
The phrase "digital signature" is used for two different things, and the gap between them is the whole subject. One is a picture of your signature placed on a page. The other is a cryptographic operation that binds a document to a key and makes any subsequent alteration detectable. Our tool does the first. If you need the second, no free browser tool provides it, and this page says which software does and why the distinction matters more than it sounds.
In This Guide
Three tiers, not two
Most articles present a binary: electronic signature versus digital signature. European law is more useful than that, and its three tiers are a good way to think about the problem regardless of where you are.
- A simple electronic signature. Any electronic mark indicating intent to sign: a drawn squiggle, your typed name, an image pasted onto the page. It carries no evidence of who made it. This is what our tool produces, and what Preview, Markup and every free annotation app produce.
- An advanced electronic signature. Uniquely linked to the signatory, created using means under their sole control, and linked to the signed data such that any later change is detectable. In practice this means a certificate and a private key. This is what Acrobat's certificate signing and dedicated e-signature platforms produce.
- A qualified electronic signature. An advanced signature made with a qualified certificate issued by a qualified trust service provider on the relevant national trusted list, using a qualified signature creation device. Under the EU eIDAS Regulation this is the only tier that is explicitly given the same legal effect as a handwritten signature throughout the Union. You cannot produce one with software alone; it involves an identity check by a provider.
The practical reading: the higher the tier, the less you need to prove separately if the signature is challenged. A simple signature may well be enforceable, and if someone denies making it you will be arguing about surrounding evidence rather than pointing at the file.
Placing a signature, free and locally
Our sign tool runs in the browser, so the document is not uploaded anywhere. That matters here more than for most operations, because the things people sign are contracts, offer letters and tenancy agreements rather than brochures.
1 Open the tool and add the PDF
Nothing is transmitted. The file is read from your disk into the page. No account is needed.
2 Draw, type, or upload
Draw with a mouse, trackpad or touchscreen and pick the ink colour and weight. Or type your name. Or upload a PNG or JPEG of a signature you scanned once, which gives a much better result than drawing with a mouse. Avoid WebP, which does not currently embed correctly and can vanish from the downloaded file.
3 Position, then download
Drag to move, drag the corner dot to resize, press Delete to remove. Zoom in before positioning if you are on a phone, because signature lines are small. The signature is flattened into the page at download, so it becomes part of the page graphics and cannot be moved or deleted by the recipient.
Two details worth knowing. Uploaded signatures are remembered in your browser, up to six of them, on that one device only; they are not synced anywhere and clearing site data removes them. And the free plan allows three operations per day with files up to 50 MB, counted at download, so signing and adding a date in one session costs one operation.
The best-quality route for a drawn signature, incidentally, is not to draw it in software at all: sign a sheet of white paper with a black pen, photograph or scan it, crop tightly, and upload that once. It will look like your signature because it is your signature, and you can reuse it.
What each platform already offers
macOS
Preview's markup toolbar has a proper signature feature with two capture methods: draw on the trackpad, or hold a signature written on white paper up to the camera, which Preview traces and cleans up. It stores signatures for reuse and works entirely offline. On a Mac this is the best free option and there is little reason to use anything else for placing a signature.
iPhone and iPad
Open the PDF in Files, tap Markup, then the plus button, then Signature. Fully local. On an iPad with an Apple Pencil this produces the most natural-looking drawn signature available anywhere, because you are actually writing.
Windows
There is no dedicated signing feature, but Microsoft Edge's built-in PDF viewer has a Draw tool that can be used to sign and then save the file, entirely locally and with nothing installed. Acrobat Reader also offers free signature placement. A browser tool works too, and is the right choice if you want to reuse a scanned signature image across documents.
Android
Xodo and Acrobat Reader both place signatures for free. Zoom in first; placing a signature accurately with a fingertip on a phone screen is harder than it sounds.
The thing that silently breaks certificate signatures
This is the most useful piece of practical knowledge in this whole subject, and it is almost never mentioned.
A certificate-based signature in a PDF works by hashing a defined byte range of the file and storing the result inside a signature field. Its guarantee is precisely that those bytes have not changed. So if you take a certificate-signed PDF and do almost anything to it, the signature breaks and readers will report it as invalid. That includes:
- Merging it with another document.
- Compressing it, particularly with anything that re-renders pages.
- Flattening annotations or form fields into the page.
- Re-saving it from a tool that rewrites the file rather than appending to it.
- Printing it to PDF, which produces an entirely new file.
Our tools rewrite the document, so putting a certificate-signed PDF through any of them will invalidate the signature. This is not a defect in either the file or the tool; it is what a signature is for. Proper multi-party certificate signing works by appending incremental updates so that each signature covers the state of the document as the previous signer saw it, and only software built for that will get it right.
So: sign last. If a signed document needs an appendix added, the appendix is added before signing, or the document is signed again afterwards by everyone.
Legal validity, more precisely
"Electronic signatures are legally binding" is true and too broad to act on. Two clarifications.
In the United States, the ESIGN Act and state adoptions of UETA give electronic signatures and records the same effect as paper ones, but not unconditionally. The elements that matter in practice are intent to sign, consent to transact electronically (which for consumer transactions carries specific disclosure requirements), association of the signature with the record it signs, and the ability to retain and reproduce the record. A drawn mark satisfies the form requirement. Whether you can later prove who made it is a separate question, and it is the question that actually gets litigated.
In the EU, eIDAS does not say all electronic signatures are equivalent to handwritten ones. It says a qualified electronic signature has that equivalence, and that a signature must not be denied legal effect solely because it is electronic. Those are different statements, and the tiers above are the reason the distinction exists.
Categories where a handwritten or notarised signature is still commonly required include wills, codicils and testamentary instruments, some family law documents, various court filings, certain real property transactions, and specific regulated contexts such as pharmaceutical records. This varies by jurisdiction and none of this is legal advice.
The practical rule: for a routine agreement between parties who both want the deal, a drawn signature is fine and has been for years. For anything you can imagine someone denying later, use a platform that records an audit trail of who signed, when, from where and what they were shown, or certificate-based signing that makes tampering detectable. We provide neither, and would rather tell you that than sell you a picture of a signature as security.
Place a signature without uploading the contract
Draw, type or reuse a scanned signature image, entirely in your browser. Best result: photograph a real signature on white paper and upload it once.
Open the sign toolFrequently Asked Questions
How do I add a signature to a PDF for free?
On a Mac, Preview's markup toolbar has a signature feature that can capture your signature from the trackpad or through the camera, entirely offline. On iPhone or iPad, use Markup in the Files app. On Windows, Edge's PDF viewer has a Draw tool, or use a browser tool. RaptorPDF's sign tool lets you draw, type or upload a PNG or JPEG signature image and runs in the page with nothing uploaded, which matters because the documents people sign tend to be confidential.
What is the difference between an electronic and a digital signature?
An electronic signature is any electronic mark showing intent to sign, including a drawn or typed one, and carries no evidence of who made it. A digital signature is a cryptographic operation: a private key signs a hash of the document, so a verifier can confirm the document has not changed since signing and that the key is bound to an identity by a certificate. EU law splits this further into simple, advanced and qualified signatures, and only the qualified tier is given the same legal effect as a handwritten signature throughout the Union.
Does RaptorPDF support certificate-based digital signatures?
No. It places a drawn, typed or uploaded signature image on the page and flattens it into the document. There is no certificate, no tamper detection and no audit trail. For certificate signing use Acrobat or software with access to a signing key; for an audit trail use a dedicated e-signature platform.
Why does my PDF say the signature is invalid after I edited it?
Because a certificate signature guarantees that a specific range of bytes has not changed, and editing changed them. Merging, compressing, flattening, re-saving or printing to PDF will all invalidate it, including through our tools, which rewrite the document. Sign last. Proper multi-party signing appends incremental updates rather than rewriting the file, and only software built for that handles it correctly.
Are electronic signatures legally binding?
Generally yes, with conditions. In the United States, ESIGN and UETA require intent to sign, consent to transact electronically with specific disclosures for consumer transactions, association of the signature with the record, and the ability to retain the record. In the EU, eIDAS says a signature cannot be denied legal effect merely for being electronic, and separately gives qualified electronic signatures equivalence with handwritten ones. Wills, some family law documents, certain court filings and various regulated contexts are commonly excluded. This is not legal advice.
How do I get the best-looking signature?
Do not draw it with a mouse. Sign a sheet of white paper with a black pen, photograph or scan it, crop tightly, and upload that image once; it can then be reused. On an iPad with an Apple Pencil, drawing directly is equally good because you are genuinely writing rather than steering a cursor.
Related Resources
- Sign PDF Tool — Draw, type or upload a signature
- Complete PDF Signing Guide
- PDF Editors for Legal Documents
- PDF Security Guide
- Protect PDF — Add a password before sending