Head over to the AppExchange and search for Formstack Documents or go to https://appexchange.salesforce.com/listingDetail?listingId=a0N3000000B53bmEAB to get started.
Sign in as a System Administrator for the Salesforce Org that you’d like to install Formstack Documents for Salesforce.com.
Once you’re logged in, you’ll be presented with details on what will be installed into your Salesforce Organization.
After reviewing, click Confirm and Install.
Installed and ready to go!