Does this happen with all files or just one specific file ? If all files can you find any common font or graphic on the documents ? If you can examine your fonts to make sure the ones you have are not corrupt.
What settings are you using for Export to PDF ?
If it is a multi page document that keeps crashing can you try exporting each page to see if one specific page crashes ? Then it would be an image or other on that page.
Send over a copy of the document if you can and we can see if it crashes here. If all files then I would look at your fonts very closely - have you installed any new fonts ? Remove them.