Adobe Acrobat 7 Professional - Manual (Page 634)

Removing PDF/X information
You can remove all PDF/X-specific information, such as the output condition or the
GTS_PDFX version key. This is useful if a PDF/X-compliant file has been modified, if
you want to start over, or if an ICC profile increases the file size too much.
To remove PDF/X information:
1. In the Preflight dialog box, click the Remove PDF/X icon . A PDF/X-compliant file
has a green checkmark in the lower right corner of the icon.
2. When prompted, click Yes.
The green checkmark is removed, and the tool tip next to the icon says "Not a PDF/X file."