PDF/X is an ISO-standardized subset of PDF designed for reliable print production exchange. The "X" stands for eXchange. PDF/X ensures that a document sent to a commercial printer will reproduce correctly, addressing common print production issues: missing fonts, RGB-only content in CMYK print workflows, unembedded color profiles, and interactive features that don't apply to print.
Key PDF/X versions: PDF/X-1a (all colors converted to CMYK or spot colors, all fonts embedded, no transparency), PDF/X-3 (allows ICC-based color management with RGB content), PDF/X-4 (most modern, allows native transparency, layers, and CMYK+spot colors with ICC profiles). PDF/X-4 is the current standard for professional print workflows.
If you're submitting files to a print shop, they may require PDF/X-compliant files. Creating PDF/X requires print-production software: Adobe InDesign, Illustrator, or Acrobat Pro. Online tools including FileCurve produce standard PDFs, not PDF/X — for professional print submissions, use the native export settings of your design software.