It is rare to find downloadable textbooks, written by Nigerians, online. Except for some poetry collections.

My take: Having loads of e-books or PDF files on your phone doesn't guarantee you success in your field. You feel you'ld gain more knowledge by reading, but being realistic; you are putting yourself in undue stress. You never get to finish one completely, you keep skipping pages.

Instead of looking for where to download heaps of textbooks online, kindly make use of libraries at your reach; better still buy the hard copies of those books.

Well if you're still bent on having them, I know sites you can visit.