RAR archive of 13.4 MB for the Dell OptiPlex All-in-One 7420. The name does not say what is inside, so it may hold a schematic, boardview, BIOS image or a mix, and it should be extracted and inspected before use. For an all-in-one desktop such material is typically used to diagnose power, display backlight and boot issues on the integrated motherboard. Whatever the content turns out to be, confirm that the board number on the PCB matches the documentation, and back up any flash chip before reprogramming 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 @biositechyangiyer. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.