PDF/X-4 vs a Regular PDF for Print
PDF/X-4 is not simply “a PDF with high resolution.” It is a standardized print-exchange condition that constrains and describes what a receiving print workflow can expect; an ordinary PDF can be printable, but it does not by itself assert PDF/X-4 conformance.
Use the numbers from your actual job
The guide explains the decision; the linked calculator gives you the value for your own file or production assumptions.
PDF is a container; PDF/X is an exchange condition
ISO 15930-7 defines PDF/X-4 for dissemination of digital data intended for print reproduction. The important difference is conformance to a print-exchange specification, not the filename extension.
Visual appearance is not enough
Two PDFs can look identical in a viewer while differing in output intent, page boxes, embedded resources or other print-production conditions. Preflight exists to inspect those underlying properties before they become production defects.
PDF/X-4 is not a universal printer setting
A printer may require a specific PDF/X flavor or a more detailed workflow profile. GWG PDF/X-Plus specifications add market-segment preflight expectations on top of the base exchange standard, so the receiving workflow remains the controlling requirement.
Practical answer
PDF/X-4 is not simply “a PDF with high resolution.” It is a standardized print-exchange condition that constrains and describes what a receiving print workflow can expect; an ordinary PDF can be printable, but it does not by itself assert PDF/X-4 conformance.
When the decision affects a paid print run, book upload, client order or expensive material, keep the calculation with the job notes and verify any external specification again immediately before production.