File Extensions
When you create a file with a program and save it, the file name will be saved with a file type extension. The file will be saved with the icon of the program used to create it showing in your folders.
Eg. You used MS Office Word to create a document named ‘Letter’ so the file is now
Letter.docx
Images have their own types of extensions i.e .jpg
Videos and Audio files have their own types as well i.e .wmv or .mp3
It’s important to be aware of this for many reasons. The best reason is that there will come a time that you can’t open an attachment on an email you have been sent – it happens to everyone. to explain further…
If someone emails a file attachment or copies a file onto your hard drive from their computer, you need to have the program they used to create it (or a compatible one) installed on your computer as well to be able to open the file
Some file types (extensions) can be opened with a number of different programs and some can’t. To help you recognize files and the programs that will open them on your computer refer to the guide I have uploaded for you, (click on the links I have included to find out more…)

There are a lot of file extensions out there and what you explained is just a fraction of them
I suggest searching for a file extension resource database whenever you see a file extension that you have no clue about.
Even ones that are known to you, might get confusing at times.