Small 42.2 KB PDF filed as a schematic for the 3N256 part. Under the JEDEC system the 3N prefix marks a registered device with four leads, and the same size across 3N253 to 3N259 suggests these files repeat a shared family datasheet. Technicians open such sheets in a PDF reader to check terminal assignment, absolute maximum ratings and the case outline before fitting a replacement. Make sure the exact number on the fitted component matches, since grades within the family differ in limits.
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.