Listed as a schematic, this 553 KB PDF named 29040a is most probably a datasheet revision for a 4 Mbit 29-series parallel flash part, the a suffix suggesting a later edition or variant. Its size matches the plain 29040 file, so the two may be near duplicates. The sheet serves to confirm pin functions, supply voltage and erase or program commands before dumping or rewriting an old firmware chip. Save a verified copy of the original contents first, and check the marking on the package against the document.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.