Bearing only the part code 2SJ438, this 416 KB PDF is indexed as a schematic, yet the 2SJ prefix in Japanese JIS designation identifies a P-channel field-effect transistor, so a datasheet is the likely content. It is the reference to consult for breakdown voltage, drain current, threshold and RDS(on), together with pinout and package dimensions, when testing a suspect device or selecting an equivalent. Any PDF reader opens it. Confirm the marking and case of the original part, since suffixes can alter ratings.
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 @cyberlanelectonik. 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.