Briefcase can be used to share and manage documents that you create in Briefcase or document and images that you upload to your Briefcase. Briefcase lets you save files in your account so that you can access these files whenever you log in to your account from any computer.
You can upload documents, spreadsheets, presentations, images, pdf files from your computer or your computer network and you can save attachments sent with your email messages to a Briefcase folder. You can create different briefcase folders to organize the files.
Files you upload to Briefcase are copies of the original file on your computer. Changes you make to a file in your briefcase does not change the original file.
Zimbra Help document: Working in Briefcase
Did You Know? Collaborating with the Zimbra Briefcase