If for some reason you have to change, add, or remove a file type’s association, then you can use the command line tool assoc which is inbuilt in Windows Vista.
Note : You must have administrator credentials for changing, adding or removing file associations.
- Open an elevated command prompt Windows. To know how read this.
- To list all the current file associations type assoc and press Enter.
- To remove a file association with a file extension, type assoc followed by extension and an equal sign. For example, if you want to remove file association of .txt files, type assoc .txt= and press Enter.
- To associate a new file extension with a filetype, type assoc followed by extension, an equal sign and then the file type. For example, if you want to add file association of .txt files to OpenOffice, type assoc .txt=OpenOffice.org.doc and press Enter.
- To modify or change a file extension with a filetype, type assoc followed by extension, an equal sign and then the new file type. For example, if you want to modify file association of .txt files to Notepad, type assoc .txt=txtfile and press Enter.