Is there an easy way to shorten polylines once they have been created? So far the only way I have found is to drag the endpoint of the line and drop it perfectly over the vertex point. This is problematic because it's almost impossible to get the two points to perfectly over lap, so I end up having to delete the whole line and recreate with the correct amount of vertices.
Right now, there is no X & Y position or Length property for Polylines in Acrobat. The closest you can get is to use Rulers & Grids and set your Grid Increment. If you do that, you should go to View > Show/Hide > Rulers & Grids > Snap to Grid.
To set the Grid Increment choose Preferences > Units & Guides.