OnePager will import the critical path from Microsoft Project, Project Server/Project Online, Smartsheet, or Primavera P6 and highlight it on your project timeline:
Tasks that are on the critical path will be highlighted with a red (or other custom color) stripe along the top. Summary tasks that contain critical children will have their critical paths displayed based on which children are critical and which are not.
If you are importing from Microsoft Project, OnePager will use the Critical field, but can be configured to use a number of other custom critical path calculations if desired. Smartsheet automatically calculates your critical path, and OnePager will display your critical path based on Smartsheet's analysis. If you are importing from Primavera P6, the XER format will support critical path, but XML does not.