What "digital signature" means in everyday use
Colloquially, a digital signature just means signing a document electronically instead of with pen and paper — drawing your signature with a mouse or finger, typing your name in a signature-style font, or uploading a photo of your handwritten signature. That's what most people mean when they search for this, and it's what PrivaPDF's sign tool provides.
There's a stricter technical meaning too: a cryptographic digital signature that uses a certificate to mathematically bind a signature to a specific signer and detect any later tampering with the document. That's a different, more specialized process (used for code signing, for instance) and isn't usually what's needed for signing a lease or a contract.
How PrivaPDF applies it
Your signature — drawn, typed, or uploaded — is composited onto the page and flattened permanently into the PDF's content, so it can't be casually dragged off or edited afterward, all done locally with the file never leaving your device.