PDF datasheet-style file for the 2SB1290 transistor, only 38.7 KB, so likely a brief sheet of a few pages. The name carries no other details such as package or maker. By the JIS convention, a 2SB number identifies a PNP bipolar transistor of the low-frequency class, common in audio and power-switching stages. Repairers use such a sheet to read pinout, maximum collector current and dissipation, and to choose a suitable replacement. Diode-test the junctions in circuit and compare against the expected PNP behaviour.
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.