Hi akela! Unfortunately, setting up margins is not available yet for PicoPDF. You may use the Move Content feature instead to move elements instead of using tab or space bar to align a text or group of words. For more details you may check this link: http://help.nchsoftware.com/help/en/picopdf/win/move.html
Also, we would be glad to take your suggestion so our developers can improve the software for better user experience. You may leave suggestion/s on this link: https://www.nch.com.au/suggestions/index.html?software=PicoPDF