Ground resistance reference map for the iPhone 7 Plus RF section labelled LATCP_RF, according to the Chinese title, in a 10.2 MB PDF. Technicians use it to compare their measurements on RF components and lines against expected values, narrowing down no-service or weak-signal faults. It opens in any PDF viewer. Results depend on meter type and measurement mode, so verify the board variant and, where possible, cross-check against a working iPhone 7 Plus board before replacing parts.
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 @uzb4422. 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.