If you are working towards this achievement, you might have already followed a guide. If you haven't, you'll need to go back for the 91 original manuscript pages anyway. Realistically, you cannot follow a video guide or individual item type list for your "collectibles" run through this game.
Tyger7 has a great walkthrough available in a zipped doc here: http://www.xbox360achievements.org/forum/showthread.php?t=23...
I recommend using Dropbox or email to send this doc to your iPad/mobile device, so you can play in the dark!
Specifically for these pages, they're mostly in plain sight. I do recommend keeping a guide near, though. There are 15 pages only available in nightmare mode (for a total of 106).