Ok, maybe I have got the solution. I have read a bit more about PDF/X and found that PDX-1a just allows CMYK. Thats what the printing company asked for...but looks like this is the issue as the PNG file is RGB. So I used PDF/X-3:2002 and that worked as it allows RGB too. Funny enough PDF/X-4 does not work...funny
shows everything converted to RGB (as the PNG File is RGB). Looks like PNG will not get converted to CMYK, instead the whole file will be converted to RGB.
Two parts here.
A raster image inside PNG is no more PNG or JPG or whatever... It is a raster image inside a PDF.
The real problem here is that you are not using the correct PDF export setting.
A PDF ...
Some clarifications first.
I am aware that CMYK is a Colour Gamut used for Printing
@User287001 (btw, this user should put a name behind all that knowledge) already said that it is not a gamut.
CMYK is several things.
A. It is a Color model, generally speaking using primary subtractive colors to generate an image based on a light substrate. The K is ...
You have not mentioned anything about the color profile.
My usual example:
Take a marker and draw a line on a coated magazine paper, and on a newspaper. The ink value is the same, the color is not.
Leave your color as Pantone, the point of Pantone is that tries to be an "absolute color".
Define a set of color profiles, for example, Swop2, ...
The issue has not a thing to do with color spaces. It is about transparency...or alpha. Use BMP format. You cannot readily composite using chromakey or alpha blending with any other format on Windows based machines.
Broadly speaking there are two schools of thought on file-format design.
One is that you should have lots of options to give lots of different users what they want. The problem with this approach is that compatibility becomes a problem. Just because a program advertises support for tiff files doesn't mean it can open your particular tiff file.
The other is ...
Because PNG is a lossless raster image format developed for the web, and ultimately for display screens which are RGB.
However the format was never intended or designed to be a print format, and therefore doesn't need to support CMYK colour, and so it's entirely the wrong format to use for CMYK printing - i.e printing where separations are required ...
Look at it this way: PNG was developed as a replacement for GIF and so generally to be used in digital work, which means RGB (screens use RGB). And yes PNG is limited to RGB. While CMYK is a print-specific model available in JPG**, TIFF, PSD and some other formats. Read: