The quick overview is that you just need to keep both .app bundles available on your Mac, so you can launch either app as desired. Your documents will be accessible from either version and will preserve their complete contents and formatting. You can safely open and edit documents in either version without any fear of data loss or other incompatibilities.
The only caveat is that you should not launch both versions of Nisus Writer simultaneously. You should only interleave your usage of different versions (eg: always quit version 2 before you launch version 3). If you accidentally launch both versions simultaneously nothing serious will happen as a result. But there might be some contention for settings and files, aside from it being confusing if a single document is open for editing in multiple apps.
How to Install Version 3 and Keep Version 2:
If you have Nisus Writer Pro installed already and want to try version 3 without disrupting your existing app, here's what to do:
1. Download the zip archive of Nisus Writer Pro version 3.
2. If your web browser didn't automatically expand the .zip archive, then expand it manually (eg: double-click it in the Finder).
3. Move the expanded Nisus Writer app to any folder where you'd like to keep it, just don't replace your existing Nisus Writer app.
You can now launch version 3 from wherever you moved it, or launch version 2 from its preexisting location (likely your Applications folder). You might want to keep both app icons in your Dock, so you can easily launch either version. You can do so by right-clicking an app icon and choosing the "Keep in Dock" option:
- dock.png (140.54 KiB) Viewed 21729 times
The app icons for version 2 and 3 are distinctive. Version 2 shows Hermes (aka Nisus Man) fully, while version 3 shows an inky pen.
What Happens to Settings Between Versions?
The first time you launch version 3 your settings and preferences from version 2 will be automatically imported.
However, once the initial import occurs your settings will diverge between versions 2 and 3, if you continue to use both of them. The two app versions (mostly) store their settings in different locations. This was done partly because version 3 adds support to sync your settings via cloud services like iCloud Drive.
NOTE: customizations involving files like templates, macros, and glossaries are not affected. You can use exactly the same template files in version 2 and 3, just like any other documents.