This is likely macOS only. The Number of Pages field in New Document doesn't accept the value unless you explicitly change focus away from the field before clicking Create.
File > New
Click the Pages tab
Note the number in the Number of Pages field and then change it to something else - don't tab out of the field or press Return
Click the Create button - Publisher will create a new document with the number of pages set to the prior value of the field
If you create another new document, the default value will be what you typed last time.
Thanks