PDF schematic of about 157 KB labelled 2G-IOT, revision 1.4, which matches the naming of the Orange Pi 2G-IoT board, though the file name itself states only the 2G-IOT model and version. Pages of this kind show the power tree, processor and memory hookup, cellular modem circuitry, SIM socket and header pinout. Use it to trace a dead rail, check the modem supply or follow GPIO wiring to the expansion connector. Verify that the revision silkscreened on the PCB is V1.4 before relying on part values or net names.
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 @boardview. 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.