I'm guessing you mean these— https://i.ebayimg.com/images/i/332226796510-0-1/s-l1000.jpg —primarily created for storing magazines and periodicals. They are available in metal, plastic and boxboard/cardboard. For under sink storage I think the plastic is best; it won't rust or soak up water should there be a leak. Nonetheless, I do not think of them as being good for undersink storage. There are racks and platforms that would make better use of the space. Even a couple of dishpans to contain cleaning solutions and tools would be better IMO.
Another thing you can do under the sink, is get some vinyl tiles from Lowes or Home Depot and put them on the shelf for easy clean up. Do not do what I did and get a pattern, just get the cheapest ones you can find without a pattern. Makes clean up a breeze.
I agree with Mindshift that book files might not be that useful under a sink. Although, depending on their size, they could work to stand boxes with plastic wrap, aluminum foil, storage bags, etc. Here's a small sink that uses tension rods and baskets to organize under a sink. You could also build custom shelves to fit that area. There are a lot of commercial products available for under sink storage so if those ideas won't work, try using your search feature to search Under Sink Storage to see what's available and how you can create something similar as a DIY project. Wishing you the best.
Here are some options. Maybe not exclusively book files but they do come in handy for sure when separating different products.