I'm not really intending this for print.
All the images on the particular pdf I sent you are from the web.
OK. Then all the images are going to be RGB at 72dpi. Between your images and what you've done to open the file in Preview the quality has suffered.
I'm not sure this is this is the problem, but the way I opened them in preview was just by changing the file extension.
Yes, this is most likely the problem. If you mean that you saved a Pages file and then changed the extension to .pdf then because Preview is an Apple program it was able to open the file and it displayed it at low resolution.
Just changing the extension of a file does not change the filetype. If I replace .txt on a text file with .jpg I do not all of a sudden have a jpg of a text file that I can view in Photoshop. Preview might see that it's a text file and MAKE a viewable jpg out of it but that's something entirely different.
Which explains why Acrobat Pro won't open it. It's a Pages file renamed as a PDF. It's not really a PDF.
In Pages you are probably going to want to export the file as an actual PDF and make sure that you have some higher quality settings checked.