printing two 8.5 x 11 pages as a 11 x 17 using indesgin

Working with an older file and can not figure out how to get the side by side 8.5 x 11 pages to save as a 11 x 17 in PDF format The indesgn file looks right and the older PDF files were saved correct but I do not know how the previous person saved this. When I go to print the updated file It prints on two 8.5 x 11.