You might try GoodReader. It has a reflow mode (where you can adjust text size), margin cropping, PDF link support and much more. In non-reflow mode, it does maintain the cropping margins you define from page to page.
The only app that can view Adobe DRM PDF's at all on iOS that I know of is Bluefire, if that's a requirement for you. It's not a great reading experience (doesn't allow you to set cropping margins that persist, and frankly seems to have performance issues), but it's good to have the option available when you need it (e.g. U of Chicago Press has a free ebook every month, often in PDF format, but they are DRMed, so I use Bluefire for these).
Last edited by tomsem; 02-14-2011 at 12:50 AM.