A.nnotate should belong to a relatively small category of tools. Its functions are not very powerful, but it is sufficient. If you do not register, you can try it simply, but the functions are greatly discounted. You can only simply apply the document tagging function. Therefore, I still recommend that everyone use it after registration. All you need is a valid email address. Registered users have two major tagging features: 1. Document tags, you can upload your documents. Currently supported formats include PDF, doc, ppt, xls, OpenOffice. 2. Webpage screenshot tags, you can make some notes on your important webpages. Just input the URL, A.nnotate will automatically take a screenshot for you, and then you can add tags at will.