A simple way of adding the version number in your content would be to create a new project property which you can then use anywhere in your content (Topic Titles, other Project Properties, in the Topic Editor etc.).
To do this, go to Project Settings, and under Project Properties click the New toolbar button to create a new property (e.g. "VersionNumber"). Once the Project Property has been created, set the value (e.g. v1.0). You can change this value as the version updates.
To include this value in your content, go to your Build Profile (either for Web & CHM or PDF), and select the Properties page. Edit the Copyright Notice property to add the version number as follows:
You can also include the version number anywhere in the Topic Editor by surrounding with double % characters (e.g. "Current version: %%VersionNumber%%"
Any time you want to update the version number you just need to update it once in the Project Settings editor.