To run IDImposer, first open the Document that you wish to impose.

THEN:

In InDesign, open the Window > Utilities > Scripts panel. You should see now see ‘IDImposer 11 – XXXX Edition’ entries in the Applications folder of the Scripts Panel, where ‘XXXX’ is ‘Booklet’ or ‘Pro’.

Double-click ‘IDImposer 11 XXXX Edition.jsxbin’ in the Scripts panel.

OR

Script Bay, a great alternative to InDesign’s Scripts Panel can be found here:

http://in-tools.com/

With Script Bay, you can store scripts and run them from any folder on your computer.

THEN

Choose your imposition settings (or Apply a Preset), and click the “Impose” button.