If you are unable to download the BIRT RCP Designer templates saving these in .rtpdesign format this is due to the browser in use. If you are using Internet Explorer or FireFox you may notice the option to download and save these files is not available. These templates appear in XML format. When launching SCTM using the Google Chrome browser, you will then be able to download the documents without further issue.
Another option if you are using FireFox or Internet Explorer is to open the report Template in XML format. It is possible to use the Browser to save the files adding the file format .rtpdesign. This will then appear in the correct format.