Electronic signatures and digital signatures are often conflated but represent fundamentally different concepts in document authentication. Understanding the distinction, the underlying technology, and the legal frameworks is essential for anyone using signatures on PDF documents, whether for contracts, regulatory filings, or everyday business correspondence.

An electronic signature is broadly defined as any electronic indication of intent to agree to or approve the contents of a document. This includes typed names, drawn signatures on a touchscreen, scanned images of handwritten signatures, checkbox confirmations, and even email confirmations. The defining characteristic is intent, not technology. When you draw your signature on a PDF using a signature tool, the result is an electronic signature — a visual representation of your signature embedded as an image or drawing annotation in the PDF file. The PDF contains no cryptographic proof of identity; the signature's validity depends on the circumstances and context in which it was applied.

Digital signatures, by contrast, use public key infrastructure (PKI) to create a cryptographically verifiable proof of the signer's identity and the document's integrity. The process works as follows: the signer has a private key (kept secret) and a corresponding public key (shared through a digital certificate issued by a Certificate Authority). To sign a PDF, the signer's software computes a hash (a fixed-size fingerprint) of the document's content, then encrypts that hash with the signer's private key. This encrypted hash, along with the signer's certificate, is embedded in the PDF in a signature dictionary. To verify the signature, a reader decrypts the hash using the signer's public key from the certificate, computes a fresh hash of the document, and compares the two. If they match, the document has not been altered since signing and the signature is authentic.

PDF signature fields are specialized form fields (widget annotations with a field type of Sig) that define the signature's visual appearance and contain the signature dictionary with cryptographic data for digital signatures. The visual appearance is defined by an appearance stream — a content stream that renders the signature's visual representation, which might include the signer's name, the signing date, a signature image, and validation status indicators. For electronic signatures without PKI, the signature field contains only the appearance with no cryptographic data.

The legal validity of electronic signatures is established by legislation in most developed jurisdictions. In the United States, the Electronic Signatures in Global and National Commerce Act (ESIGN Act, 2000) and the Uniform Electronic Transactions Act (UETA) establish that electronic signatures cannot be denied legal effect solely because they are electronic. In the European Union, the Electronic Identification and Authentication Services Regulation (eIDAS, 2014) defines three tiers: simple electronic signatures (any form), advanced electronic signatures (uniquely linked to and capable of identifying the signatory), and qualified electronic signatures (created using a qualified signature creation device with a certificate from a qualified trust service provider). Only qualified electronic signatures are automatically equivalent to handwritten signatures across all EU member states.

Certain document types and transactions may still require specific signature forms. Wills, powers of attorney, certain real estate documents, and some government filings may require notarized or witnessed signatures depending on jurisdiction. However, for most commercial contracts, employment agreements, purchase orders, and business correspondence, electronic signatures created by tools like this one are fully legally binding and enforceable.