Zotero allows the collection of citations to any kind of material and automatically formats bibliographies in almost any style. Zotero also has many search, tagging, and note taking features.
Note that Zotero supplies 300 MB of free storage for PDFs, images, web snapshots, and any other Zotero files. Individual subscriptions for additional storage space are available.
Plagiarism is a very serious academic transgression. Copyright law, and exceptions such as fair use, can be complex. To learn more, check out the following resources: