PDF document for the 2SA1635, filed under schematics but in fact a component sheet for a discrete transistor; the _1-2 suffix in the name likely marks a part or revision of the document without saying which. Under the Japanese JIS numbering, the 2SA prefix denotes a PNP transistor intended for high-frequency use. At 57.6 KB it is a short document. Technicians open such a sheet in any PDF reader to confirm pinout, package and maximum ratings before fitting a replacement part on a board.
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.