You may be converting a document that contains numbers in parenthesis.
For example: (12345.00)
However, you prefer to have that number set as -12345.00.
First, select the columns that need to be corrected and apply a Number or Current format to them.
Select all columns that are in the Number or Currency format.
Remove the checkmark from "Preview sizes, colors" on the Preview Pane toolbar. Leaving this active will allow you to see the data as it is shown on the PDF, which we do not currently want.
Go into the Options > Format and place a check in the box labeled "Replace parenthesis with negative sign".
Make sure that your Excel settings are also formatted for currency/number or you may see the parenthesis in your output.