Filed under schematics, this 357 KB PDF is named after the 25AA640 and 25LC640, which are Microchip SPI serial EEPROMs of 64 Kbit capacity, so it is most likely the manufacturer datasheet. Expect pinout, SPI command set, status register bits, write timing and voltage ranges. Technicians consult it when reading or rewriting such a chip with a programmer such as a CH341A, or when checking chip select, clock and data lines on a board. Save a copy of the original contents before any write.
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.