New Idea - Online PDF Store. Is it legally acceptable?

Today I saw one website sell one book PDF in cheap rates.

If same idea if we implement for selling online what about it????

My idea is that...to sell the PDF of reference books of all stream of engineering in the form of pdf @ cheap rates (approximately 30/- to 40/-)....i know one website where all books PDF i can get....it is absolutely free and this will be captured by me...those PDF I'll upload in the website with rates given...due to free of cost for me to attract people many offer such as first two books free, refer and earn and so much... This website is mainly for engineering student of all branches...they get easily at least 5 reference book of one subject..this will help those to find easy in one website.

is it legally acceptable?????