Apple iPhone 4 repair archive in RAR format, only 870 KB in size, with the name giving nothing beyond the model. A pack this small likely holds a single schematic or boardview file; extract it with WinRAR or 7-Zip to confirm. Such documents let a technician find parts, follow power rails and data lines and look up test points while fault finding. GSM and CDMA versions of the iPhone 4 use different boards, so compare the board markings with the files before relying on them.
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 @esquematicosparatodos. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.