PDF filed as a schematic under the name 28C256, the widely used 256 Kbit parallel EEPROM part code. At 159 KB it likely includes pinout, page write mode, data polling, toggle bit and timing diagrams, although the name does not state the vendor or package. Repair work uses it when reading firmware from older equipment, burning a replacement with a universal programmer or confirming pin compatibility with EPROM sockets. Check the speed suffix and maker on the chip, and keep the original dump before erasing.
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.