The file extension you supplied is invalid. It must e.g. not contain special characters like ", *, :, <, >, ?, \, /, | or spaces. It must also be less than 20 characters long.
File extensions are used to help Windows find and launch the correct program when you click on a file. For example, if you click on a .PDF document, Windows will automatically launch a PDF viewer if you have one installed.
First of all, you should rename your file so it does not contain invalid characters, and then try opening it with a generic file viewer to inspect its content. In that way you may be able to determine what type of file it really is.
Try a universal file viewer