A 92.7 KB PDF catalogued as a schematic, named 28C257, a code from the 28C series of parallel EEPROM memories. The name gives no vendor, speed grade or package. The document should detail pin functions, supply voltage, write cycle timing and any software data protection scheme. Technicians use such sheets to confirm compatibility with a programmer and to check whether a 28C256 or similar part could substitute. Compare the chip marking with the sheet and back up existing contents before reprogramming.
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.