ECMS-6329: Failed to view big MS Office files with PDFViewer

Problem analysis:
* When a file is too big, JODConverter fails to generate the corresponding PDF file.
  That raises exception in PDFViewer when getting the maximal Page number of PDF file.

Fix description:
* Invoke JODConverter only when the original file is small enough (5MB).
* Handle correctly when there is no PDF file from JODConverter.