This document is intended to serve as a short description of the data files of the catalogue of 88883 stars of the Henry Draper Extension Charts. Detailed explanation of the Extension, catalogue production and so on may be found in the printed paper referenced above. There are two files comprising the catalogue, namely data file (CATALOG) and individual remarks file (REMARKS). The format of the second one is free - it starts with 6-digits HDE number followed by remark text. The CATALOG file contains 88883 logical records of the length 61 bytes each. A detailed description of the record format is given below. Abstract of Paper: The Henry Draper Extension Charts (Cannon et al., 1949), published in the form of finding charts, provide spectral classification for some 87000 stars mostly between 10th and 11th magnitude. This data, being highly valuable, as yet was practically unusable for modern computer-based astronomy. An earlier pilot project (Roeser et al. 1991) demonstrated a possibility to convert this into a star catalogue, using measurements of cartesian coordinates of stars on the charts and positions of the Astrographic Catalogue (AC) for subsequent identification. We present here a final HDEC catalogue comprising accurate positions, proper motions, magnitudes and spectral classes for 86933 stars of the Henry Draper Extension Charts.