PDF
The Portable Document Format (PDF) is a file format created by Adobe Systems in 1993 for document exchange. PDF is used for representing documents in a independent document format. The documents are viewable and printable on any platform — Macintosh, Microsoft® Windows®, Linux®, and many mobile platforms.
To view a PDF you need a pdf reader. There is an offical reader from Adobe or there is a lightweight alternative called foxit reader. It you require an open source program there is GSview .
RSS
RSS (which stands for "Really Simple Syndication") is a web format used to publish frequently updated content such as blog entries, news headlines or podcasts. An RSS document, which is called a "feed", "web feed", or "channel", contains either a summary of content from an associated web site or the full text. RSS makes it possible for people to keep up with their favorite web sites in an automated manner that's easier than checking them manually.
RSS content can be read using software called a "feed reader" or an "aggregator." The user subscribes to a feed by entering the feed's link into the reader or by clicking an RSS icon in a browser that initiates the subscription process. The reader checks the user's subscribed feeds regularly for new content, downloading any updates that it finds.
Firefox , the popular web browser has RSS-compatibility built in. If you are looking for a standalone RSS reader, RSSOwl is another option.