Microchip PIC16C6x family datasheet, a 2.64 MB PDF covering several related 8-bit OTP or EPROM microcontrollers grouped under one x placeholder. The name does not state which revision of the document this is. It serves as a reference for pinouts, port functions, timers, oscillator configuration and DC characteristics when tracing a circuit or checking whether a controller is receiving proper power and clock. Match the exact suffix and package on the chip to the right table, since pin counts vary between family members.
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 @datasheet. 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.