A schematic diagram for Apple hardware (board 820-3486). Shared as “iPhone_6_820-3486_Brd+Schematics_2.pdf” — a .pdf file, 3.76 MB.
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 @ShareMan_Electronic_Files. 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.