PDF support

Is there a way to both download pdf files from the internet and view then on the ipad? I know that there are a variety of programs that allow you to view PDF documents but all the ones i have see involve using a computer to put the pdf files onto the ipad. Also the PDF files can only be accessed through a series of web portals with the original needing a login and password.is it possible access and download these through the ipad alone and then view and edit them and save them on the ipad? I need to be able to do this on only one device as i usually need to access research materials while on the go ( on the 2 hour bus ride ) and PDF is the academic standard for files.