Legal document is a legal instrument a legal term that is used for any formally executed written document that can be formally attributed to its author, records and formally expresses a legally enforceable act, process, or contractual duty, obligation, or right, and therefore evidences that act, process, or agreement. Examples include a certificate, deed, bond, contract, will, legislative act, notarial act, court writ or process, or any law passed by a competent legislative body in municipal (domestic) or international law.

With the onset of the Internet and electronic equipment such as the personal computers and cell-phones, legal instruments or formal legal documents have undergone a progressive change of dematerialisation. In this electronic age, document authentication can now be verified digitally using various software. All documents needing authentication can be processed as digital documents with all the necessary information such as date and time stamp imbedded. To prevent tampering or unauthorized changes to the original document, encryption is used. In modern times, authentication is no longer limited to the type of paper used, the specialized seal, stamps, etc., as document authentication software helps secure the original context. The use of electronic legal documents is most prominent in the United States' courts. Most American courts prefer the filing of electronic legal documents over paper. However, there is not yet a public law to unify the different standards of document authentication. Therefore, one must know the court's requirement before filing court papers.

To date, the variety (and inadequacy) of the definitions used for digital signatures (or electronic signatures) have produced a legal and contractual minefield for those who may be considering relying on the legality and enforceability of digitally signed contracts in any of many jurisdictions. Adequate legislation adequately informed by cryptographic engineering technology remains an elusive goal. That it has been fully, or adequately, achieved (in any jurisdiction) is a claim which must be taken with considerable caution.