When the PDFViewer is created and a file is loaded using the fromFile method a new thread will be created. That thread remains in memory and doesn't get destroyed when the entire widget is destroyed.
$("#pdfViewer").data("kendoPDFViewer").destroy(); $("#pdfViewer").empty();
That created thread remains in memory and doesn't get destroyed.
The thread should get destroyed when the widget is destroyed.
###Workaround
A possible workaround:
kendoPDFViewer.processor.pdf.loadingTask.destroy();
The issue should be additionally researched as there are some leftovers in the JS Heap even when the workaround is used.