You can upload a PDF, a sound or video or other file, and add it to a list by using the "Create" option.
First select "Type" (article, book, website, etc.) by clicking the down caret to the right, to bring up the appropriate fields for that type of source (journal title, etc.). Then add title, author, and other bibliographic information.
Drag or browse for the file you want to upload, then select which section to add it to, and click to "Add."
You can also use Create to add an item to the list that is not in the library collection. When you "Publish" the list or "Send to Library," the library will attempt to acquire the item to put it on reserve.