Aslam o Alikum,
Scribd is considered as Youtube of online documents and PDF books moreover note that I don't upload documents there to make money actually there is a feature in Scribd website that allows the uploader to revise or reupload an updated version of the document uploaded earlier if he wants without losing his prior link. That's why I upload documents and notes there so they can be updated and uploaded again without loosing the weblink. I think now you people got my point.
Come to the next point now that is it necessary to become a Premium User to download material from Scribd?
certainly not.
If you people are facing difficulty in downloading the above said books and material then explore below link. Every step is explained there with pictures so you'll get it easily how to download for free without paying anything to scribd owners.