Definition
PDF/X
PDF/X is the ISO 15930 family of PDF standards for sending files to print: every font embedded, colour defined for the press through an output intent, and the trim and bleed declared in the file. PDF/X-1a allows only CMYK and spot colours; PDF/X-4 adds live transparency and colour management.
A general PDF can carry screen colours, missing fonts and no idea of where the page is cut; PDF/X rules those out so a printer's prepress can plate the file without guessing. The output intent is the part most people miss: an embedded colour profile that says which printing condition the file was prepared for, such as a generic CMYK or a named one like FOGRA39 or GRACoL. Print-on-demand platforms such as KDP accept ordinary PDFs and convert them; offset and many local printers ask for PDF/X, and some name the exact variant and profile.
Related tools & guides
The press-ready file, made for you
Upload your Word manuscript: Ceeryo typesets it and gives you a CMYK PDF with black on the K plate, a PDF/X output intent, crop marks and 3 mm bleed — and the plain PDF for KDP from the same upload.