Archive for the P8B75-V carrying the 1.00 suffix, presumably the first board revision, stored as a 147 KB RAR. No document type is stated in the name, so unpack it to confirm the contents before use. At this size it is likely layout or reference data rather than firmware. Later revisions 2.00, 2.01 and 2.04 are catalogued separately and may differ in component placement, so check the revision marked on your motherboard and only use this file if it reads 1.00.
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 @schematicslaptop. 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)