How do I display negative numbers with parentheses? e.g. (1,000)

The data type is Currency or Date/Time can be set the formatting. Available in Ver.2.0 or later.

Word/PowerPoint/PDF

Merge Fields Format

{!Object API Name.Field API Name, Format;Minus Format, Rounding Mode}

e.g. {!Case.TestCurrency__c, #,##0;(#,##0)}

Value: -1234

Result: (1,234)

Excel

Merge fields cannot be formatted. Set from Excel's cell formatting.

Instruction manual