Acrobat converts a whole Excel sheet to PDF even though one wants to convert only a defined print area (if converting the Excel file with either right-click or from within Acrobat . Converting from within Excel works.)
-> Applies for Excel 2010 only .
Activate in Excel the function "Allow changes by more than one user at the same time" under:
Tab Review > Share Workbook > set checkmark at "Allow changes by more than one user at the same time"
then save the document and now creating a PDF with each of the above mentioned methods works as expected.