A small PDF of 40.7 KB for the 2SA1538, a JIS-coded transistor; despite the schematic label, a file named only by part number is normally a datasheet. The 2SA prefix denotes a PNP transistor rated for high-frequency operation. Use it to read absolute maximum ratings, electrical characteristics and the pin assignment of the package, which matters when testing in circuit with a multimeter in diode mode. Check the exact marking on the original component, since gain-class letters can differ.
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.