How do I create a PDF report in landscape mode?

To create a landscape PDF document, set the document's page width larger than it's height.

Commons page size (A3, A4, A5, Letter, and Legal) is predefined in the UniPDF library for setting the page size.

Use those predefined page sizes to create a landscape document by switching the width and height value.

c := creator.New()
pageSize := creator.PageSize{creator.PageSizeA4[1], creator.PageSizeA4[0]}

For a complete example see this code: