The reason there's no single solution is because error 8 is a totally generic message - it simply means there is something corrupted in the PDF file's data. Could be any one of thousands of possible causes.
As a side note if a PDF form suddenly grows to a huge size, it invariably means that you've chosen a typeface for one of the form fields that's equally enormous. Arial Unicode is the prime culprit on Windows - unless you need the full international code pages, swap to Helvetica instead.