Someone sends you a PDF and asks you to sign and return it. The obvious approach — print it, sign it, scan it back — is tedious, produces a worse-looking document, and requires a printer you may not have. The alternatives are better, but they are not all the same thing, and the difference matters more for some documents than others.
Two things called signing
An electronic signature
This is a mark you place on the page: a drawn signature, a scanned image of one, or your name set in a handwriting-style typeface. It is placed at the right spot on the right page and becomes part of the document.
What it proves, on its own, is intent. It shows that whoever produced this document meant to signify agreement. It does not prove who did it, and it does not prove the document has not been altered since — an image can be copied off one PDF and pasted onto another in about a minute.
A digital signature
This is cryptography rather than imagery. The signing software computes a hash of the document, encrypts that hash with a private key belonging to a certificate issued to you, and embeds the result in the file.
Any reader can then verify two things independently: that the document has not changed by so much as one byte since signing, because the hash still matches; and that the signature was made with the private key belonging to a named certificate, which a certificate authority issued after checking identity.
That is a much stronger claim. It is also more involved — you need a certificate, which means an identity check and usually a fee, and the recipient needs a reader that validates it.
Which one does the job?
Far more often than people expect, an electronic signature is what is actually being asked for. A delivery acknowledgement, an internal approval, a rental application, a school consent form, a supplier questionnaire — these want a signed-looking document from a person they are already in contact with, not cryptographic proof of identity.
Reach for a digital signature when the document will be relied on by someone who does not know you, when it is likely to be contested, or when a specific standard is required — property transfers, regulated filings, high-value contracts, anything where a rulebook names the requirement. In those cases the requirement will usually be stated explicitly, and if it is not stated, asking takes less time than redoing it.
Laws differ by country, and both kinds of signature are widely recognised in one form or another — but the details vary enough that this is worth checking for anything consequential. We build PDF tools, not legal advice; for a document that matters, ask someone qualified in your jurisdiction.
Signing without an account
Sign PDF handles the electronic case. You draw your signature with a mouse, trackpad or finger, or upload an image of one, place it where it belongs, size it, and export. It is the same operation as printing and scanning, minus the printer, the scanner and the loss of quality.
A few practical notes:
- Draw at a large size. A signature drawn small and then enlarged looks shaky. Draw big; scale down.
- Use a transparent PNG if you are uploading one. A JPEG will bring a white rectangle with it, which sits visibly on top of any ruled line or coloured background.
- Add the date as text. Most forms want one and most people forget until after they have exported.
- Flatten before sending. This is the one that catches people out — see below.
Why flattening matters after signing
If your signature is placed as an annotation — which is what most editors do — it remains a separate, movable object inside the file. The recipient can drag it, delete it, or in some readers simply switch annotations off and print a clean unsigned page.
Running Flatten PDF merges the signature into the page content itself. It becomes part of the page rather than a sticker on top of it. Do this before you send anything you would describe as signed.
Note that flattening is the right move for an electronic signature and the wrong one for a digital one — flattening rewrites the page, which invalidates a cryptographic signature by definition. If a document carries a verified digital signature, do not modify it at all.
Filling in the form while you are there
Many documents that need signing also need fields completed. If the PDF has real interactive form fields, fill them in your reader first, then flatten, then sign. If it does not — a scan or a flat page — you can add the text as you would the signature, positioned where the lines are.
Keeping the signature off other people's servers
Your handwritten signature is a piece of personal data with an unusually long life. It appears on your bank mandates and your passport application, and unlike a password you cannot rotate it. Uploading it, along with whatever document it is attached to, to a website whose retention policy you have not read is a poor trade for a task your own device can do.
Signing in the browser keeps both halves local: the signature image is drawn onto the page in your tab, the file is rebuilt in memory, and the download comes from the page itself. Nothing is transmitted, which you can verify from the network panel or simply by going offline first.
In short
An electronic signature shows intent and covers most everyday documents. A digital signature proves identity and integrity and is what you want when the document will be scrutinised. Draw large, use transparency, add the date, and flatten before sending — that last step is what turns a sticker into a signature.