Image signature vs digital signature: what signing a PDF really means
"Please sign and send back" usually means one of two very different things. Most of the time it means putting your signature on the page — drawing it, typing it or pasting a photo of it. Sometimes it means a digital signature, which is not a picture at all. Knowing the difference helps you choose the right one and understand what your signed PDF can and cannot prove.
An image signature is a picture on the page
When you draw your signature with a finger, type your name in a script font, or place a scanned image of your signature onto a PDF, you add a picture to the page. It looks like a signed paper document, and for many everyday purposes — a leave form, a delivery receipt, an internal approval — that is exactly what the recipient wants.
What a picture cannot do is prove anything by itself. Anyone with a copy of the image can place it on another document, and nothing in the file shows whether the page was changed after it was signed.
A digital signature is a cryptographic seal
A digital signature uses a certificate issued to a person or organisation and mathematics tied to the exact contents of the file. A PDF reader can check it and show who signed and whether the document has been altered since. Change a single character after signing and the signature is shown as invalid.
Getting one requires a digital certificate. In the Philippines, the Department of Information and Communications Technology (DICT) runs the Philippine National Public Key Infrastructure (PNPKI), which issues digital certificates; commercial providers also exist. Signing with a certificate is done in software that supports it.
What the law says, in short
The Electronic Commerce Act of 2000 (Republic Act 8792) gives electronic documents and electronic signatures legal recognition in the Philippines, so a document is not invalid merely because it was signed electronically. Whether a particular signature is accepted, and how much it proves if disputed, still depends on the transaction and on who is receiving it.
In practice: if a bank, a court, a government office or a contract specifies how a document must be signed — wet ink, notarised, or digitally signed with a certificate — follow that. When nothing is specified, ask; it costs less than signing twice.
Making an image signature as sound as it can be
Sign the final version of the document, not a draft, and keep your own copy of exactly what you sent. After placing the signature, flattening the PDF bakes it into the page so it cannot simply be dragged off or edited as a separate object in most viewers.
Treat the image of your signature like a key. Do not leave it in shared folders or send it on its own, and be wary of anyone who asks for "just your signature" as an image file.