Beginning with the October 2017 release of Bridge, a new Output workspace has been introduced to generate PDF contact sheet natively in Bridge. Get the instructions to create a PDF contact sheet in Output workspace.
The existing Adobe Output Module (AOM) plug-in is no longer supported in Bridge 2018. If you're using Bridge 2017 or earlier, you can download the Adobe Output Module (AOM) plug-in and get installation instructions.
To check your current Bridge version, choose Help > About Bridge from the menu bar.
To update to the latest version of Bridge, see Update Creative Cloud apps.