The list of entries is kept unique. That is to say, if you try to have two entries sharing the same file extension, it will replace any existing entry. This includes entries with multiple extensions. For example, if you have an entry which refers to both .DOC and .TXT file extensions and then try to add a new entry referring to just .TXT, it will replace the entry referring to both .DOC and .TXT.
You can specify where to place the attachment file name in the command line for any attachment launcher. You do this by putting a percent sign (%) where the file name should go. If no percent sign is present, the file name gets appended to the end of the command line with an intervening space. If more than one percent sign is present, only the last one will be used. When you don't use a percent sign and the file name has a space in it, the file name will be quoted. The following example shows how to always quote them:
"D:\Program Files\PMView\PMview.EXE" /NoHelp "%"