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.
To make this adjustment, you need to first select the columns in the Number or Currency format.
Remove the checkmark from "Preview sizes,colors" on the Preview Pane toolbar.
If that doesn't change the parenthesis to a negative sign, you can 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.