Hi Bodo-Lutz, PDFs can have various different kinds of objects in them but MoI will only read vector objects. That's stuff like lines that are stored as a line entity with 2 endpoints and when you zoom in on it it stays with a crisp display on the screen.

It's also common for PDFs to have bitmap images in them, but when you zoom in using Adobe Reader on those you'll see that the display gets blocky.

So most likely the ones that were not working for you had bitmap images in them and not vector objects.

- Michael