This can be achieved using a Saved Search and Transaction Body Field.
In this scenario, the two columns are named Commission Amount and Net Amount.
Create a Saved Search
Search Title: Enter Total Commission Amount Search
Click Criteria
Click Standard
Filter:
Select Type
Type: Select Invoice
Click Results
Click Columns
Field:
Select Commission Amount
Summary Type: Select Sum
Click Available Filters
Click Filter
Filter: Select Internal ID
Click Add
Click Save
Create a Saved Search
Search Title: Enter Total Net Amount Search
Click Criteria
Filter:
Select Type
Type: Select Invoice
Click Results
Click Columns
Field:
Select Net Amount
Summary Type: Select Sum
Click Available Filters
Click Filter
Filter:
Select Internal ID
Click Add
Click Save
Create a Transaction Body Field
Navigate to Customization > Lists, Records, & Fields > Transaction Body Fields > New
Label: Enter Total Commission Amount
Type: Select Currency
Store Value: Remove Checkmark
Click Applies To
Sales: Enter Checkmark
Click Validation & Defaulting
Search: Select Total Commission Amount Search
Click Save
Create a Transaction Body Field
Navigate to Customization > Lists, Records, & Fields > Transaction Body Fields > New
Label: Enter Total Net Amount
Type: Select Currency
Store Value: Remove Checkmark
Click Applies To
Sale: Enter Checkmark
Click Validation & Defaulting
Search: Select Total Net Amount Search
Click Save
Edit the Transaction Form PDF Layout
Navigate to Customization > Forms > Transaction Form PDF Layout
Preferred Invoice PDF Layout: Click Edit
Click Add Custom Element
Choose Element(s): Select Total Commission Amount
Click OK
Click Add Custom Element
Choose Element(s): Select Total Net Amount
Click OK
Click Save