Preview allows you to add the image to the PDF as a new page via drag and drop:

1. Open the target PDF in Preview.
2. Open the image in a new Preview window via "File" menu > "New from Clipboard".
3. In both windows, click "View" menu > "Contact Sheet".
4. Drag the image thumbnail from one window into the PDF thumbnails in the other window; the image will be added to the PDF as a new page.

This method also works if you want to add pages from one PDF into another.

Preview allows you to add the image to the PDF as a new page via drag and drop:

1. Open the target PDF in Preview.
2. Open the image in a new Preview window via File > New from Clipboard.
3. In both windows, click View > Contact Sheet.
4. Drag the image thumbnail from one window into the PDF thumbnails in the other window; the image will be added to the PDF as a new page.

This method also works if you want to add pages from one PDF into another.