What is Digital signature?
A digital signature is a cryptographic seal that binds a signer's identity to the exact contents of a document. Unlike a typed name or scanned image, it's mathematically tied to the file — any change after signing breaks the signature.
Digital signature vs electronic signature
The two terms get used interchangeably but mean different things. An electronic signature is any mark indicating consent — a typed name, a scanned image of a handwritten signature, a click on an "I agree" button. A digital signature is the strongest form: a cryptographic operation using a private key that produces a tamper-evident seal. Every digital signature is electronic, but not every electronic signature is digital.
How a digital signature on a PDF works
When a signer applies a digital signature, the signing tool computes a hash of the PDF's contents and encrypts that hash with the signer's private key. Anyone with the matching public key (usually distributed through a certificate authority) can verify two things: who signed, and that the document hasn't changed since signing. If a single byte of the PDF is altered after signing, verification fails.
Why filling order matters for signed PDFs
If you sign first and then try to fill fields, you break the signature — because filling changes the document content, which invalidates the cryptographic hash. The correct order is fill, then sign. Some workflows treat fillable fields as exceptions (form-fill changes don't break the signature if the signing tool was configured to allow them), but the safest pattern is to complete all data entry, flatten the form, then sign.
How FillWizard fits into a signing workflow
FillWizard handles the filling step. Drop a PDF, fill from a profile, export a flattened PDF that opens cleanly in any signing tool. Signers then apply digital signatures in DocuSign, Adobe Sign, or any other compliant signing platform. The exported PDF preserves the document content as plain page graphics, so the signature seals exactly what you and the recipient agreed to.
Related terms
- PDF form flatteningFlattening a PDF form merges the filled-in field values into the page content itself. After flattening, the fields are no longer editable — the values become part of the document permanently, and the file opens identically in every PDF reader.
- AcroFormAcroForm is the original PDF form technology built into Adobe's PDF specification. An AcroForm PDF embeds fillable field objects — names, types, positions, default values — directly inside the PDF structure, so any modern PDF reader can detect and fill them programmatically.