Datasheet-style PDF of 166 KB for the 2N4125, with an RE suffix appended to the part number; the name does not explain it, so treat it as a possible alternate or revised edition. The index places it under schematics. JEDEC 2N numbers are made by multiple suppliers, and the document is mainly useful for pin identification, maximum ratings and gain figures. Opening it in any PDF viewer, compare it against the plain 2N4125 sheet in this collection if values seem inconsistent with the 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.