Someone asks you to “sign the PDF and send it back”, so you draw your signature on it and save. Later, another office asks for a “digital signature” and turns down the same kind of file. Both used the word signature, but they meant two different things.
This guide explains the difference in plain technical terms: what a visual signature is, what a certificate-based digital signature adds, how to tell which one a PDF carries, and what to ask before you sign something important. It does not tell you what is legally valid where you live. That depends on local law and on the person or institution receiving the file, and only they can answer it.
Two things called “signature”
A visual signature is a picture on the page. You draw it, type it in a handwriting-style font, or upload a photo of your signature on paper, and it is placed on the page like any other image. It looks like your signature because it is a copy of it. Most everyday paperwork asks for this kind.
A digital signature (sometimes called a certificate-based or cryptographic signature) is not a picture at all, although it often comes with one. It is a block of data stored inside the PDF, calculated from the exact contents of the file and from a digital certificate that belongs to the signer. A certificate is issued by a certificate authority, a company or public body that checks who you are before issuing it. In some countries a national ID card or a government app can provide one; elsewhere you get one from a commercial provider.
The words are not used consistently: “electronic signature”, “e-signature” and “digital signature” mean different things to different laws, companies and apps. When someone asks for one, ask which of the two they mean.
What a visual signature can and can’t show
A visual signature is quick, free and works everywhere. Any PDF reader shows it, and it prints exactly as it looks on screen.
What it cannot do, technically:
- It does not prove who placed it. A picture of a signature can be copied from one file to another, just as a paper signature can be photocopied.
- It does not detect changes. If someone edits the text of the document after you signed, nothing in the file records it. The signature image stays exactly where it was.
- It carries no date you can check. A date written next to it is just more text on the page.
None of this makes it useless: for many documents, a signature everyone can see and print is all anyone asks for. But it is evidence in the way a signed photocopy is, not a sealed, verifiable record.
What a digital signature adds
A certificate-based digital signature is designed to answer the questions a picture can’t:
- Who signed. The signature is tied to a certificate that names the signer, and a PDF reader can check that certificate against the authority that issued it.
- Whether the file changed. The signature covers the exact bytes of the document. If anyone changes the content afterwards, even by one character, a reader that checks signatures reports that the document has been modified since it was signed.
- When it was signed, if the signer used a trusted timestamp. The time then comes from a timestamp service, not from the signer’s own computer clock.
Many digital signatures also show a name, a date or a handwritten-looking image on the page. That part is decoration; the proof is in the data behind it.
How to tell which one a PDF has
The page alone can’t tell you. A drawn signature and the visible part of a digital signature can look identical.
- Open the file in a reader that checks signatures. Adobe Acrobat Reader, which is free, shows a bar at the top such as “Signed and all signatures are valid”, or a warning if something is wrong. Its Signatures panel lists each signature, who made it and whether the document changed afterwards.
- Click the signature on the page. In a reader that supports digital signatures, a real one opens a window with the certificate details. A picture does nothing, or can be selected like any other image.
- Don’t rely on a browser’s built-in viewer for this. Browser PDF viewers often show signatures without checking them, so a valid one and a picture look the same there.
Why editing breaks a digital signature
Because a digital signature covers the exact contents of the file, a change after signing does not go unnoticed. Even harmless-looking changes count: adding a page number, rotating a page, merging the file with another, or adding a second, visual signature. Depending on how the change was saved, a reader that checks signatures either reports the signature as invalid, or reports that the document was changed after it was signed.
That has two practical consequences:
- If you receive a digitally signed PDF, keep the original. Our tools, like many simple PDF tools, write out a whole new copy of the file, and in that copy a reader will report the earlier digital signature as invalid, because the document is no longer what was signed. Some desktop programs can add changes on top of a signed file instead, but they still show that it changed after signing. Keep the untouched file as your record, and send the original when someone needs to check the signature.
- If a document needs both kinds, the visual one goes first. Put your drawn signature, dates and any filled-in details on the page, then apply the digital signature last, so it covers the finished file.
Adding a visual signature, and making it stay put
For the everyday case, the free Sign PDF tool places a visual signature on any page, and the file stays on your device the whole time.
- Open Sign PDF and choose your file.
- Press Add signature. Then Draw it with a mouse or finger, Type your name in a handwriting-style font, or Upload a photo of your signature on white paper. The white background is removed automatically.
- Drag it onto the signature line. The corner handles resize and turn it.
- Use Add date or Add initials if the document asks for them.
- Press Save signed PDF and download your file.
Sign PDF draws the signature into the page itself, not as a separate note that could be dragged around, so it stays where you put it in every reader. If the same document has form fields you filled in, or notes and highlights, you can fix those into the page too with Flatten PDF, so the answers can no longer be changed by just clicking a field. Be clear about what that does and doesn’t mean: it makes the page look settled, but it is not a seal. Someone with an editing program can still change the page, and nothing will detect it. Only a digital signature records that the document changed.
PDFSahl makes visual signatures only. It does not issue certificates or create certificate-based digital signatures, and the Sign PDF page says so.
What to ask before you sign something important
The technical difference is only half the question. The other half is what the person or institution receiving your file accepts, and that varies between countries, sectors and even departments. Before you sign anything that matters, such as a contract, a financial form or anything official, ask them directly:
- Do they accept a drawn or typed signature on a PDF, or do they need a certificate-based digital signature?
- If they need a digital one, which kind of certificate do they accept, and do they provide a way to get it or a platform to sign on?
- Do they also need the original on paper, a witness, or an in-person signature?
Their answer settles which kind you need.
Quick answers
Is a drawn signature the same as an electronic signature? It depends on who is using the words. Many people call any signature made on a screen “electronic”, while laws and platforms define the term in their own ways. Ask the recipient what they need, using the two descriptions in this guide.
Can I tell if someone changed a PDF after I signed it? With a visual signature, no, not from the file itself. Keep your own copy of what you sent. With a digital signature, a reader that checks signatures shows whether the file was modified after signing.
Does flattening make a PDF tamper-proof? No. It fixes form answers, notes and highlights into the page so they are no longer separate items, but the page can still be edited, and nothing records the change.
Is my file uploaded when I sign it here? No. The signature is placed inside your browser, and the document never leaves your device.