Using the Page Break Element in your Document Template Editor will allow you to insert blank pages.

Middle of document:

To insert a blank page between two existing pages or between existing content you will need to drag and drop two Page Break Elements to the same spot.

Bottom of document:

To insert a blank page at the end of your document you can drag and drop the Page Break Element to the bottom or simply click the Page Break Element and this will add it to the bottom automatically.