How can I remove the vertical and horizonal lines from the Mathcad 15 worksheet?
You can change the page format from letter of A4 to A1
Or even larger. The options you get when you select "File"-"Page Setup"-"Paper - Size" depend on the printer you selected. A lot of pdf printers will allow you to chose really huge paper sizes.
Keep in mind that you may run into problems when you try to really print a worksheet formatted that way on physical printer.