I found an issue with the HTML to PDF conversion in a Text element.
I have some old HTML chunks that were generated using SharePoint's rich text web tool. It is terrible HTML as you can imagine.
I tried to place it into a PDF and was getting an object is null error. I tracked it down to some bad tags in the source HTML. Basically if the source HTML has an tag that does NOT have a src attribute, the PDF gives an error when Save is called.
I fixed my code by adding src attributes as needed.
I would not call this a bug as the true problem is terrible HTML from SharePoint's rich text field control, but it is something that could be trapped for easily.
Just a note to help make your product better.