Importing participant data is done from within the Plan Sponsor. Because you have the Plan Document Open, you must "swap" over to the Plan Sponsor.
A user may not have both the Plan Sponsor and any of its Plan Documents open with edit access at the same time. This is because there are some shared data elements between the two (Reported Amounts for example). Therefore, if you try to open both a document and sponsor at the same time, the second tab that you open will be opened read-only.
The easiest way to swap over to the Plan Sponsor is to double-click on the Sponsor's name in Item Explorer. This will prompt you about swapping and then open the Plan Sponsor.
To import the initial participant data into DB Precision, you will first need to create an Import Definition. To do this, right-click Import Definitions on the Sponsor tab. Then give the newly created definition a name (the standard name for the initial import is "InitialImport_yyyy" where yyyy is the year of the conversion).
To specify the layout for this Import Definition, double-click on single row found immediately below the name of the newly created Import Definition. This will open the Import Row Screen.
For Reported Amounts, select the Reported Amount once. You will later be prompted which years you are importing (from and to).
When pressing OK on the wizard screen, you will see the items that you chose listed in order in the Row Items list. To view the details of a specific item, double-click that item.