Apple iPad 3 logic board boardview in .pcb format, roughly 21.4 MB, marked (1) in its name, which hints at one of two copies of the same board view. A boardview lets a technician find any part by reference, highlight nets, see pin-to-pin connections and locate measuring points when chasing a short or missing voltage. The format is opened in boardview programs such as OpenBoardView or FlexBV. Verify the board matches the third-generation iPad before relying on component positions.
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 @boardview. Enginerys does not host this file.
How to open a .pcb file
In repair archives a .pcb is typically an XZZ (XinZhiZao) boardview — popular for phones and recent laptops.