The options in the WinZip Context Menu (the menu that displays when you right click a file or folder) change depending on what you right click. Right clicking on a .txt file or a folder will cause Add to options to appear. But if you right click one archive file, such as a ZIP file, WinZip will not show Add to entries, but will show Extract to options. This applies to all file types that WinZip will open. Some of these, like ISO files often can be compressed further in a ZIP file. If you select more than one archive files, multiple different files, or a folder, the Add to options in the WinZip context menu will appear. If you want to compress just one archive file using the context menu you can do so by creating your own Send To command. To do this you should download and install the WinZip Command Line Support Add-On and follow the steps presented in WinZip's custom tutorial.