Is it on a CD/DVD?

Looks like it is on a media which does not allow you to write on...
Which OS you are using?

You may check the properties of the folder which contains the file.

"How to uncheck read-only from my disc" wrote:

The read-only box on my excel spread sheet is not checked. But when I save
it to my disc, then enter changes on it, I get a message that the folder is
marked as read only. Upon looking at properties of that file, I see a light
gray read only box that is checked. I can not access that box. How do I
prevent the checkmark in the read-only box, or remove it after it is there?