When viewing a list of files, on your Windows or Mac computer, you will usually see a small icon (picture) next to the file name. This is the program that is associated with that file e.g. a .docx file is a Microsoft word processing file and will often have the Microsoft Word logo as its icon (or the Apple Pages icon on a Mac).
Trying to open this file will launch your default word processing software and load up the document.
An unknown file type will normally have an icon that looks like a blank page. This does not always mean that your computer cannot open the file; it just means that your computer does not recognise it and may not have opened one of these files before. Unless a program, such as Word, tells your computer that it knows what this file is - your computer cannot associate it with a particular program.
Trying to open this file will often launch a "File not recognised" dialogue window. Both Windows and Mac will offer you the option to search for a program or app to open the file, but this is not always successful.
Viewing the File Extension
If your computer is set to show you the file extension - you will be able to see it after the file name whenever you open a folder of files in Windows Explorer e.g.
If you cannot see file extensions, then the following steps will enable this function:
Windows 10 and 11
- Start Windows Explorer (you can do this by opening up any folder)
- Click the View tab at the top of the window
- Tick the box for File name extensions
In Apple Finder, select Preferences and tick the Show all filename extensions option:
Before and after
Before the file type extension is visible, all you can see is the file name and an icon for any associated program. This is only useful for files that your computer already recognises:
After the file type extension is visible, you can now try to find a program that will open your "unknown" files:
In this case, I have an unknown .xfd file type.
What will open this file type?
FileInfo.com provides a database of over 10,000 file type extensions.
A simple search box allows you to input the letters of any file extension.
It will then tell you all about the file and gives you a list of programs that will open it (where available) on Windows, Mac and Linux.
In the case of my .xfd example, this is a data file that can be opened with Adobe Reader.