The 24WC257 is a Catalyst Semiconductor I2C serial EEPROM, and this 55.6 KB PDF, though catalogued as a schematic, is almost certainly its datasheet. The 257 numbering indicates a 256 Kbit class device, and the document should describe pinout, address inputs, write protect function and page write behaviour. A technician uses it to select the correct chip type in programmer software, check the two-wire bus wiring, and compare it against the related 24WC256. Read and archive the existing contents before any rewrite.
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.