Labelled only 28256, this 181 KB PDF is indexed as a schematic, though its number points to a datasheet for a 28-series 256 Kbit parallel EEPROM; the manufacturer and package are not given. It serves for checking pin functions, read and write timing and write protection when handling the chip in a universal programmer. The size matches the 28512 file, so confirm the content actually covers this part, and compare with the larger 28256a edition. Always save the original data first.
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.