MyDraw supports native export of any drawing to PDF. To do so click File -> Export -> PDF. The following dialog will open:

The PDF export dialog lets you configure the page size, orientation and page margins and shows a preview of the export. You can also specify the print layout that determines the zoom mode of the diagram. If the paging mode is set to "Fit To Pages", you can specify on how many pages the diagram should be spread over. For example if you want the diagram to fit on 1 page, set page columns and page rows to 1. If you want the diagram to span on 6 pages, set the page columns to 3 and page rows to 2, and so on. When ready, click the Export to PDF button to export the diagram to a PDF file.