I've a problem with PDFCropper 1.63 with certain PDFs which return "java.lang.NullPointerException" on cropping. It worked very well with similar PDFs from the same publisher, but their recent files return just that error. I noticed that publisher has changed the PDF version from 1.4 to 1.5. PDFCropper.log file includes this line "java.lang.NullPointerException at org.pdfbox.pdmodel.PDPageNode.getAllKids(PDPageNod e.java:194)"
However, I tried to convert/merge that problematic PDF with the free pdfsam 2.0 app. It produced the same PDF (v1.5), but this time PDFCropper worked just fine.
Hope this helps someone.