Why do I get Multiple PDF files from a single Excel file?

Every now and then, when you try to print an entire Excel file to an Adobe PDF file, you'll notice that it'll start printing to multiple PDF files.  


This is because not all the worksheets in the workbook are the same dpi. 


I've noticed that 600 dpi seems to work best for all the files.  This
setting can be found in the "Page" tab of the "Page Setup" option in
the "Print Quality" prompt under the "Paper size:" prompt.