PDF files can also be created simply from photos or images, and evidence of this can be found in this Image to PDF Converter program.
With Image to PDF Converter you can convert any photo (in any of the following formats: JPG, GIF, TIFF, JP2, PNG, PCD, PSD, TGA, BMP, DCX, EMF, WMF, ICO, PPM or PNM) directly into a PDF document, and you can even join different images together in the same PDF.
Image to PDF Converter can also be run from the Windows command line. You can also do batch processing to speed up the whole task.