Sometimes when downloading assets as JPEG or PNG files on Mac, they may save as PDF files instead. This can be frustrating, especially if you need the file in its original format.

It is possible that the file association for JPEG and PNG files has been changed to open with Preview, which is a PDF viewer on Mac. You can try changing the default program that opens these files.

To change the default program for a specific file type:

1. Select a file of the type you want to change (in this case, a JPEG or PNG file).
2. Right-click on the file and choose "Get Info" from the menu.
3. In the Info window, expand the "Open with" section.
4. Choose the program you want to use to open this file type.
5. Click the "Change All" button to apply the change to all files of this type.