Hey, we'd like to be able to add pictures as PDF files too. We're just getting started and we've had to focus on getting the first few things right. Also, there's a number of nifty workarounds to convert PDF images into PNG or JPG file formats you can use with Ponga.
Most PDF readers, including Adobe Acrobat Reader allow you to export image files from individual PDF pages. On a Macintosh, you can use Preview to open the PDF file then select the area you’re interested in and use the Export feature to create an image file from it. Notice that Preview lets you set the resolution and file size.
Generally, the larger the file size, the higher the resolution of the resulting image. A great tool is Smallpdf.com that makes it easy to create a set of image files from a large, multi-page PDF document. (Oh, and as of this writing, the tool is free! What's not to like about that.)
If creating Ponga pictures from PDF files is really important to you, reach out to email@example.com or via the chat window and let us know. I can already tell you we'll be sympathetic.