Archive for the Apple iPhone 4S in ZIP format, 1.33 MB. Only the model appears in the name, so its exact contents are unconfirmed; packages of this kind usually contain a schematic, a boardview or component layout images. They are used to locate parts on the logic board, trace backlight, charging and power circuits and find test points while measuring voltages or diode readings. Compare the board markings with the document, since iPhone 4S boards differ from the earlier iPhone 4 despite looking similar.
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 .zip file
Compressed archive that every operating system opens without extra software.