Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

 

You can use those materials as long as they are referred to their original publishers or writers. It is common that people use those materials at different website for general viewing or browsing.

 

You are sinful in case you quote those materials either for academic or commercial purposes without referring to their original authors.

 

Allah Almighty knows best.