Thank you for writing.
PDF format provides a big variety of compressions allowing the file producer to maximally optimize the result file size. The explanation for the slow rendering of PDF files is highly dependent on the concrete case. We have seen examples of files with really big monochrome images which are compressed with BitsPerComponent
equal to 1
allowing to reduce the file size a lot. Slow rendering with minimal file size may also be seen when the PDF file uses vector content that may be described with a few postscript text rows but this content requires intensive calculations when rendered in a PDF viewer (for example some pattern PDF content).
If you want us to have a deeper look at the concrete case you are mentioning, you may send us the sample PDF files.
I hope this helps. Should you have further questions please do not hesitate to write back.
Telerik by Progress