I have been working on a lengthy document for several years and all of a sudden I can't scroll down the screen using my two fingers on the touch pad, although I have no problem scrolling down this page to look for similar questions.

What version of Pages is running on your MBP?

What version of OS X is running on your MBP?

The MBP does not run iOS.

Menu > Apple > About this Mac

You have switched from Pages '09 probably, to Pages 5.6.1. Pages 5 is very inefficiently written and will bog down in larger documents with even a moderate number of objects.

Have you tried the same document in Pages '09 which is much smoother?

Peter

If you migrated from your older System, Pages '09 should be in your Applications/iWork folder.

Pages 5.6.1 > Menu > File > Export > Pages '09

gets you back to where you were, though Pages 5.6.1 will have stuffed up at least some of your files' formatting and features.

Peter

You freed up some RAM or cleared off space on your hard drive for more Virtual Memory.

Simple restarts do much the same.

Either way the problem will probably recur.

Peter