Ah! So it is a "real" percent; it translates a decimal number to percent. I thought it would just append a percent symbol onto whatever number was entered.
I suppose if I wanted the latter (just adding a percent symbol onto a numeric entry), I would have to use script, right?
To the best of my knowledge, yes you would. I looked this up in the LiveCycle Designer help, it's not a feature I'm familiar with. I found it by searching the help index for numeric, double clicking "about" and then clicking on the Numeric patterns link in the right hand pane.
In the display pattern, put the % in single quotations. So,
ZZ9.99'%'
Another option, in case you hadn't considered it, is to put a static text object to the right of your right-justified numeric field and put a % there. This simple approach makes it clear to the user what you're expecting. I like to do the same with dollar amounts (i.e. put a static $ to the left of the field).