RAR archive labelled A125M, matching the Samsung Galaxy A12 model code SM-A125M, 14.6 MB in size; the name does not say what is inside, so it may contain schematics, board images or reference values. Extract it with WinRAR or 7-Zip and inspect the contents before relying on them. Material for this model is typically used for tracing charging and PMIC rails, locating test points and checking shorts. Verify your phone is the M variant, as other A12 builds such as A125F can differ in parts of the board.
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 .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.