Schematic in PDF form for the Xiaomi Redmi 9A smartphone, with the name marking it as a PCB document. The file name gives no board number or revision, so compare the layout against the actual mainboard before trusting part references. A phone schematic like this lets a technician trace charging and power rails, follow display, camera and SIM connector signals, and work out which line is shorted when the phone stays dead. Any PDF reader opens it, and text search for net names speeds up tracing considerably.
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 @mischematic. 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.