FILE EXTENTION IS file-extension
The FILE EXTENTION clause identifies the eight-character file extension for this element. Valid values are a-z, A-Z, 0-9, or all blanks. Trailing blanks are supported, but embedded blanks are not.
So, what does this really mean? The "FILE EXT: " field on the type definition panel is ONLY used when you are adding files from or retrieving files to a local file directory using CA Change Manager Enterprise Workbench (CMEW) or the Endevor Eclipse Plug-in. The field must be set to a valid file extension type such as: doc, ppt, xls, jar, ear and so on or leave it blank. Once the value has been set and you retrieve an element to a local file system, the extension will be appended to the element name.
Suppose you have a type called WORD2007 and its extension has been set to docx. If you retrieve element MyPersonalDocument from Endevor using eclipse or CMEW, it will be stored on your hard disk as MyPersonalDocument.docx. Likewise, when you add MyPersonalDocument.docx to Endevor (to type WORD2007) the element will be stored in Endevor without the extension.
This obviously requires some caution, because if you add a file autoexec.bat to type WORD2007, it will be stored in Endevor under element name "autoexec.bat". If you then retrieve it back it will be called autoexec.bat.docx.