Small 65.1 KB PDF reference for the HEF4008BP, a CMOS logic device from the HEF4000 series that the 4008 number identifies as a four-bit full adder; the BP suffix usually marks the plastic DIL package. Though catalogued as a schematic, it is most likely the manufacturer datasheet with pinout, truth table and timing. Use it to verify supply and logic levels on the pins, check carry signals with a probe, and confirm equivalents from other 4000-series makers before swapping the chip.
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.