Small schematic PDF of about 348 KB named MV-MTK RF, which suggests a radio-frequency section of a design built around a MediaTek chip, though the name does not identify a specific device or board revision. Material like this is useful for following antenna paths, RF supply rails and transceiver connections when a unit has weak or no signal. With such an uninformative name, compare chip markings and layout on your board carefully against the drawing before using it for measurements or part replacement.
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 @datasheets1. 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.