PressPDF is an online portal for checking and correcting PDF artwork. 10 checks and 18 corrections are offered. Files up to a maximum of 500 MB can be uploaded.
During testing, I noticed that spot colors are not always recognized and when converting from RGB to CMYK, SWOP is always used as the target color space instead of the Output Intent. Furthermore, color conversion of a PDF/X file leads to loss of PDF/X conformance.
So care must be taken with PressPDF corrections…!