The root-like rhizoids of fungi penetrate a source of food, secrete hydrolytic enzymes, and absorb the end products. These activities are all involved in the process of what?
These activities mentioned in question are all involved in nutrition of fungi.
Fungi mostly have saprohytic mode of nutrition . These derive their nourishment from dead and decaying organic matter, as these can't synthesize their own food material like autotrophs. Fungi are thus saprohytes mostly.
The rhizoidal hyphae in fungi penetrate the substrate, secrete digestive enzyme which digest the organic substances present in the substrate. The digested food is absorbed by the hyphae and utilized by the entire fungal body called mycelium . The digestion is external.