This tool only changes the file extension, meaning it changes one label for another, such as changing a .jpg to a .txt.
Be careful: this is not a converter. So, if you change the label of a file from .jpg to .pdf, the file will still be an image and will not become a PDF.
It can be useful for files of the same type. For example, if you have different types of images, you can make your computer see them all as if they were of the same kind.