Very short 20.1 KB PDF for the part 27C256-12A, catalogued as a schematic. The number belongs to the 27C EPROM family, and the -12 suffix normally reflects the access-time speed grade. The A detail is not explained by the name. No board or device is mentioned. Given its small size this may be a brief or summary datasheet. Use it to check pinout and basic ratings before programming or replacing the chip. Confirm against a full manufacturer sheet when precise timing matters.
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.