John: Thanks for your reply. I saved the article on reinstalling High Sierra that the Apple agent referred me to, but have not tried reinstalling it. Frankly, it sounds a little scary and I'd hate to lose stuff.
The Pages problem started after High Sierra. A couple of years ago I had set up a custom template, which I use almost daily. It's fairly simple: body type (Helvetica 12), 18- and 14-point heds (Helvetica bold), an italic for cutlines, and some custom bullets.
The template worked just fine until High Sierra was installed. Since then, if I cut-and-and-paste type from a web page, email, etc., where the format is set for body type, I end up with Roman, not the Helvetica I want. I have to re-select the pasted type and re-format it.
Not the most earth-shattering problem (unlike my iPad, which has shut down after the iOS 11.1.2 update, but that's another story...)
Thanks for any suggestions you can give me.