The 130 KB PDF titled 2SD1348 relates to a JIS-numbered NPN bipolar transistor, the 2SD series covering low-frequency types, and is expected to be a component datasheet despite its schematic label. It is useful for confirming pinout, collector-emitter voltage, current and dissipation ratings when a transistor in a power or driver stage fails. Open it with any PDF reader. The file name gives no maker or package, so verify the device marking and case before selecting a replacement.
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.