Apple iPhone 4 schematic, called iPhone 4G in the file name, provided as a small 356 KB PDF with no board number or revision listed. The size suggests a partial or compressed set of sheets, so some circuits may be missing. Technicians use such diagrams to trace power rails, follow signals between the main chips and connectors, and find components on a shorted line. Open it in any PDF viewer. Check the logic board number printed on your phone and confirm it matches the document 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 @c_f_s. 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.