Small 37.6 KB PDF for the 2SA1900, written in lowercase in the original name and placed in the schematic category; the content is most likely a brief datasheet. Per JIS numbering, the 2SA prefix identifies a PNP bipolar transistor. A compact sheet like this usually gives key ratings, characteristics and the case outline. Use it to identify pins when probing in circuit and to check that any replacement meets the listed limits. Confirm the printed code on the board part matches before relying on it.
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.