PDF schematic labelled for the Apple iPhone 4S, about 1.34 MB. No board number or revision appears in the name, so the exact logic board version should be confirmed against the hardware. Repairers use iPhone schematics to trace power rails from the PMU, follow charging and dock connector lines, check baseband and Wi-Fi sections and identify components on a shorted line. Any PDF viewer opens it; given the small size it may cover only part of the board, so check the content and the board markings before relying on it.
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 @tamirat_moobile. 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.