The name 181rki carries no board or device model and resembles a power semiconductor part code, so this 173 KB PDF is best treated as a component datasheet although it is indexed as a schematic. The RKI naming pattern is associated with stud-mount phase-control thyristors. Use it to read gate trigger values, voltage classes and stud dimensions when repairing motor drives or rectifier bridges. Open it in any PDF reader and confirm the voltage class suffix on the device you are replacing.
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.