HI Derek,
I was just looking into this for our theming / customisation. I found:
http://tracker.moodle.org/browse/MDL-34687 which had the following CSS
#resourceobject { width: 100%; min-width:100%; max-width: 100%; min-height: 600px; }
I modified it slightly for our install / theme:
.resourcepdf #resourceobject { min-width:100%; max-width: 100%; min-height: 950px; //enough for a full A4 page }
hth,
Lael