We apologize for the delay in response to your query.
As per the description given above, that when you are trying to save an excel file to pdf then excel is crashing. However it doesn't after saving and then converting. So I assume that you are directly saving the .xls file as .pdf?
If this is the case then would suggest you to try using "Save as Adobe PDF" to get the conversion done correctly or use the Acrobat ribbon to create pdf.
Saving the excel as .pdf using "Save As" functionality is not recommended as its MS inbuilt converter and it works on different mechanism and we don't have hold on that.