If you are downloading the file: Right click on file name > Save-As > Save to Desktop (for now) > Locate File > Right Click file > Open With > Choose Program you want to open file with > Click on required program or Browse > Always use selected progrsm to open this kind of file > Click OK.
Alternate method: Open Explorer > Tools > Folder Options > File Type tab > Select File extension icon you need > change > Browse to file to open, or "NEW" > type in extension > OK > Advanced > Add Icon and title > OK > Close.
Alternate method: Open Explorer > Tools > Folder Options > File Type tab > Select File extension icon you need > change > Browse to file to open, or "NEW" > type in extension > OK > Advanced > Add Icon and title > OK > Close.