I've been a fan / user of PDF-X for ages. However I've finally found a reason (the only one!) that I have to turn to another PDF renderer: PDF X-Change seems to do some caching of a document that has been opened such that updating (overwriting) that document and re-opening shows the original version of the document. This has become evident whilst working on automation of filling in PDF form fields: after a test automation, the PDF is still displayed with the original form field values.
I'm using PDFSharp to fill in the form fields. The changes I make are visible in other readers (such as the built-in one on Windows
If I can supply any more information, please don't hesistate to ask (: