[bewitched]

I use CS (version 4) not CSII so your mileage with my answer may vary.

When you open a pdf, CS automatically rasterizes (bitmaps) the image which can change its size (and resolution). I'm guessing that your co-workers are opening and closing a different file than you-- depending upon where the image originated, how it was edited and how it was originally saved (before being converted to pdf) rasterization (and therefore size) will vary.

Having said that, I don't really have an answer about how to fix it (and my experience with pdf files, especially in CS, is extremely limited) other than to suggest that you try to resize the original image before saving it as a pdf. I'm curious as to why you are saving an image as a pdf, is it to make it easier for distribution? I don't know about CSII but, CS is not all that great of a program to use for pdf applications.


eta: Have you tried to reset the image size after opening the image? I don't remember how, but you should be able to do so.

eta2: As to file size when saving...I don't know if this will work, but you might look at whether CS is saving the pdf as a bit file. If so, try converting it to JPEG before saving and see if that keeps your file size down.