Part number 2SC3401 is the only information in the name of this 87.3 KB PDF, so no device or board is identified. The 2SC prefix is the Japanese JIS code for an NPN high-frequency transistor, which suggests a manufacturer datasheet despite the schematic category. Such a sheet gives voltage and current limits, gain ranges and pin assignment, which matter when replacing a failed small-signal transistor. Any PDF viewer opens it; compare the package type with the part on the board before substituting.
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.