When creating a Scan, Verification, Validation or Document Review activity, on the Configuration tab, you can provide only one Document or Folder variable as input to the activity. On the Input/Output tab, you can provide any number of additional input and output variables of any type, except Document or Folder variables. However, you can add fields from a Document or Folder variable.

For any activity other than Scan, Verification, Validation, and Document Review, you can provide any number of input and output variables of any type, including Document or Folder variables.