When exporting to a PDF (vector or raster type), you can specify in the Export Options dialog to either create the PDF the size of the exported objects or use the page size as specified in Surfer. Toggle Use application page size (if available) to create the PDF with the same page size as specified in Surfer and click OK.

Select Use application page size (if available) on the PDF Options page for vector or raster PDFs  to maintain the page size as specified in Surfer.

Updated September 1, 2020