ASUS X507UBR archive labelled 303, a 5.54 MB rar that most likely holds BIOS firmware version 303 for this model, though the name does not state it outright. The size fits a compressed SPI BIOS image. Such an image is used to reprogram the flash chip with a hardware programmer when the laptop will not post after a failed update. Read and keep the original chip contents, verify the board matches X507UBR and check the image size equals the flash capacity.
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 @SCHEMATICWORLD. 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.
7-ZipWinRARThe Unarchiver (macOS)