How to Make PDF/X-1a:2001 from a PDF in Acrobat Pro

I have a 174 page PDF that I need to make in the format PDF/X-1a:2001. I asked the AI and it said it could only handle 140 pages, but I've seen that it should be able to do this. Or can I bring in a Word document and make it into that PDF/X-1a:2001 format?