I am assuming you are talking about USA taxes... this is from http://www.irs.gov. State to state requirements may vary.... It doesn't specifically refer to tax documents themselves but I think you'd have a good argument
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In what format must the records be kept?
All records should be kept in a manner that ensures their complete access to the IRS for so long as they are material. While this is typically accomplished through the maintenance of hard copies, taxpayers may keep their records in an electronic format if certain requirements are satisfied.
Rev. Proc. 97-22, 1997-1 C.B. 652 provides guidance to taxpayers that maintain books and records by using an electronic storage system that either images their hardcopy (paper) books and records, or transfers their computerized books and records, to an electronic storage media. Such a system may also include reasonable data compression or formatting technologies so long as the requirements of the revenue procedure are satisfied. The general requirements for an electronic storage system of taxpayer records are provided in section 4.01 of Rev. Proc. 97-22. A summary of these requirements is as follows:
The system must ensure an accurate and complete transfer of the hardcopy books and records to the electronic storage system and contain a retrieval system that indexes, stores, preserves, retrieves, and reproduces all transferred information.
The system must include reasonable controls and quality assurance programs that (a) ensure the integrity, accuracy, and reliability of the system; (b) prevent and detect the unauthorized creation of, addition to, alteration of, deletion of, or deterioration of electronically stored books and records; (c) institute regular inspections and evaluations; and (d) reproduce hardcopies of electronically stored books and records that exhibit a high degree of legibility and readability.
The information maintained in the system must be cross-referenced with the taxpayer’s books and records in a manner that provides an audit trail to the source document(s).
The taxpayer must maintain, and provide to the Service upon request, a complete description of the electronic storage system including all procedures relating to its use and the indexing system.
During an examination, the taxpayer must retrieve and reproduce hardcopies of all electronically stored books and records requested by the Service and provide the Service with the resources necessary to locate, retrieve, read and reproduce any electronically stored books and records.
The system must not be subject, in whole or in part, to any agreement that would limit the Service’s access to and use of the system.
The taxpayer must retain electronically stored books and records so long as their contents may become material in the administration of federal tax law
