It's very unlikley that the problem is due to the PDFs. Do you have cross-references?
You might want to try doing a Save As to clear out the change information and reduce the file size for starters. You also should let us know waht version and patch of ID you have, and your OS.
Thank you Peter, I will try the Save As. I have ID CS5 and I am running Windows 7 - 32 bit, 2gigs of memory. Peter....I am having issues with AI freezing up too when I try to apply a 3D effect to a simple object. Do you think it might be a RAM issue? Also.....what is a "cross-reference"? THANKS!!!!!!!!!!!!!!!!!!!!!!!!!
Cross-references, when you set them up in InDesign, would look like "See the entry on Cross-References on page 45" and the page number auto-updates with changes in the document, so if that section gets pushed to page 47, the "see page XX" gets updated from 45 to 47. If you don't know what they are, you probably don't have 'em. I can verify that a document with large numbers of crossrefs will bog down your computer; it seems all I work on these days is long docs with lots of cross-references, and it makes me want to upgrade.
2 gigabytes of RAM is what I'd call "absolute minimum for any kind of computing on WIn7 in 2011." I think you'd notice improvements across the board if you upgraded to 8 gigs, and probably even if you bumped it to 4 gigs. However, that still may not be the cause of your slowdowns.
In order to improve performance in InDesign, you can:
Set Live Screen Draw to Delayed or Never in Edit -> Preferences -> Interface
Turn off Dynamic Spelling in Edit -> Spelling -> Dynamic Spelling
Turn off Live Preflight in Window -> Output -> Preflight
In InDesign, you can shift from High-Quality Display to Typical Display under View -> Display Performance. If you're on High Quality, shift to Typical - it'll draw images with 72ppi previews instead of at full resolution. However, if you're already at Typical, then this won't help you very much. I don't think that saving down to JPEG would help a lot, but it might - if you're watching your PDFs being drawn slowly then maybe that would increase the rate of screen draw. Much depends on the content of those PDFs, so if they're just pictures (no text, no vector art) then saving out TIFFs or JPEGs might improve matters for you. However, before leaving PDF to move to a lossy format like JPEG, I'd ask you if there might be updated video card drivers for your machine. Honestly, I can't say that a better video card would improve performance more than more RAM would, for you, but the possibility is there.
But, before you spend money - have you tried to do anything to your computer to generally improve performance? I didn't read it too closely, but this list of suggestions was one of the first hits I got when I searched for "windows 7 performance tweaks." If you've not tried anything of the sort, it may be worth a try.
I'm sure that some other posters will be able to come up with some more things to try, both in InDesign and on your install of Windows. However, even though I can't look over your shoulder... I have a hunch that your hunch is correct, that you're just running up against the limits of your hardware.
Joel.wow thank you so much! I will try all of the preference settings you
suggested as well as the Windows 7 tweaks!