A file with an .unknown extension is a Windows file that does not have a file association. It may have an .unknown extension to serve as a placeholder for the file's correct extension.

If you have a file with either no extension or an .unknown extension, you can try to view the contents of the file by opening the file with a text editor. However, if the file is saved in a binary format, a text editor will not display the file's contents correctly. If you believe you know what the file type is, you may try changing the extension to the appropriate suffix and then attempt to open the file. For example, if you think the file is a .DOCX file created by a word processor, you can highlight the .unknown file extension and change it to .docx. Then, attempt to open it with a program that supports DOCX files, such as Microsoft Word or Apache OpenOffice.