MRC is a compression technique ("Mixed Raster Content").
It basically lifts the text off a graphic onto its own layer, stores it as 1bpp which can be compressed as such, then the underlying graphic, now complete with text-shaped holes in it, can then be compressed with jpeg or something.
the problem is whatever workflow IA uses to do this dials compression to all the way to maximum which results in 1bpp text over a smeary, unreadable mess