Last night I was looking through my ebook collection trying to find some Sci-Fi to load on my Kindle. I found Red Mars in Calibre's book listing and decided I would put that on my Kindle (a classic Kindle, BTW). I set Calibre to the task of converting Red Mars from PDF to MOBI format for transferring to my Kindle. The conversion completed normally and I transferred the MOBI version of Red Mars to my Kindle. Much to my dismay the viewing the MOBI version of Red Mars only showed the Table of Contents and then displayed a message about dowloading the ebook from Amazon. Thinking that there was a problem with Calibre's PDF to MOBI conversion routine I fired up my copy of Stanza and used it to convert Red Mars PDF to both MOBI and the native Kindle format, AZW. Both these fomats behaved the same way.
I now believe that the free PDF of Red Mars is DRM'd to prevent conversion to any other format. Something all the breathless gushery about Random House's release of Red Mars seems to have missed. For now, I've not deleted Red Mars from my collection and I did download a different copy of the PDF and I'll repeat the conversion process to see if the same issue occurs.
But for now: GUILTY AS CHARGED!