Image files can be opened instead of PDF documents. Images will be converted to PDF and can be annotated right away.
Use File Open to open image files of various formats (like JPG, PNG or TIFF) instead of PDF files. After selecting an image file, either select Center image on page or Adjust page size to image size.
When selecting Center image on page, also select page background and format just like you do when creating a new document. The image will be placed in the center of the newly created page and can still be moved or resized.
When selecting Adjust page size to image size, the image will be used as a background for a new, empty page, with the exact size of the image.