PDF/X and PDF/A standards are defined by the International Organization for Standardization (ISO). PDF/X standards apply to graphic content exchange; PDF/A to long-term archiving of electronic documents. During PDF conversion, the file that is being processed is checked against the specified standard. If the PDF will not meet the selected ISO standard, a message appears, asking you to choose between canceling the conversion or going ahead with the creation of a non-compliant file.
The most widely used standards for a print publishing workflow are several PDF/X formats: PDF/X‑1a, PDF/X‑3, and (in 2007) PDF/X-4. The most widely used standards for PDF archiving are PDF/A-1a, and PDF/A-1b (for less stringent requirements).