The 71.5 KB PDF called 25L4004 is catalogued as a schematic, yet its name follows the style of a serial memory part number, so it is most likely a chip datasheet. No device or board details appear in the name. For firmware work such a document gives the pinout, supply voltage and command set, which helps when hooking up a clip and programmer to read or write the chip. Always back up the original contents before writing anything, and confirm the exact marking on the package matches this part code.
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.