When I convert Corel file to pdf, it makes corrupted PDF file.

When I convert Corel file to pdf, it makes corrupted PDF file. It is only with one particular project. I have tried other raw files - all is good.
It could be that the this particular raw file is with problems, since i copy it and re-save it every year to make printed calendar....
When I make new document and put elements from existing calendar row file - the same happens to new file.
I have tried re-saving, taking elements to new... nothing helps.