Persian-language PDF whose title translates roughly as Western hard drive repair, 377 KB in size. No model or PCB number is given, so it is likely a general guide or annotated drawing for Western Digital drive controller boards rather than one specific board. Material of this kind usually covers the 5 V and 12 V input protection such as TVS diodes and fuses, motor driver checks and common board-level faults. Read it as general background, and confirm against the PCB number on your drive before swapping components or attempting firmware work.
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 @iranianRefix. 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.