There are times when we are not quiet sure which program could be used to open a file. Worst case scenario is when the file doesn’t have an extension. Here are some ways in which you can recognize/open such files.
Try the extension at an online file extension archive.
If everything else fails open the file with a HEX editor or using Notepad. Look for the first few charecters. These will be the filetype headers in most cases. Here is a small list of filetypes and header charecters for popular file types.
|MIME type||File Extension||Starting characters|