Hi there Joyce,
I'm sorry to hear you're having trouble. Could you open the PDF file in Adobe Reader and choose File > Properties? I'd like to know what the 'Application' and 'PDF Producer' lines say for your documents that are problematic.
Are you having this problem with all files or with just files like this one? Would you be willing to share one of these files with us via the File Conversion Issue form? If so, could you be sure to reference this forum thread in your description of the issue so we can circle back?