You can not install Applications With DISM. You can create a reference image with Office installed and then capture the image.
When this is done you can patch the image with DISM
Capturing can be done on serveral differnet ways, some examples are:
- WinPE with ImageX tool (Waik contains everything you need, included guides)
- Windows Deployment Services (WDS), can create a Capture image (right click boot image)
- Microsoft Deployment Toolkit (MDT), create a Task (Guides included in MDT)