Catalogued as a schematic, this 40.7 KB PDF is named after the 2SA1540, a Japanese JIS-registered transistor part number, so it is most likely the component datasheet. Under the JIS scheme the 2SA prefix marks a PNP transistor intended for high-frequency use. Technicians open such a document in any PDF reader to check pinout, package outline, maximum voltage and current ratings and hFE grade before fitting a replacement. Confirm the marking on the device, including any suffix letter, matches the part described here.
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.