Hi Mark - when you run the Image command and push the "Add" button, the available image formats are shown in the file types section of the Open dialog, here:



Right now you can use PNG, TIFF, JPEG, GIF, or BMP image files as background images, you cannot currently use PDF files for a background image, you will need to convert the PDF to one of those other formats (I would recommend PNG) before it can be placed as a background image.

In the future I would like to add PDF as another option for background images, but it's a lot more difficult to handle PDFs in that way because PDFs can contain a variety of different kinds of data in them like vector lines, text, as well as bitmap images. Displaying a PDF means reading through all those kinds of data and then generating a picture, which is pretty different from those other formats that MoI currently supports which only contain pixel image data inside of them. That's why PDF is not currently supported as a background image - PDFs are sort of more like "structured document files" and not just a "bitmap image file".

- Michael