At a client level documents may be edited including adding new paragraphs, deleting paragraphs, changing and adding text within paragraphs and including key variables that pick up recurring data (client name for example).
This is done by selecting "Customise/Edit Page" from the bottom right corner of a Document page.
For advance editing, it is generally easiest to use the "Copy To Clipboard" feature to copy the document (with formatting intact) and pasting it into a word processor.
All editing done in year one will remain going forward - just variables will update (new year for example). To revert to the standard template delete the document then recreate it.