My document looks like this:
I save as a PDF from Photoshop, using the default High Print Quality setting. The resulting PDF looks like this:
What's going on?
Photoshop is terrible at exporting PDF files. Silly that Adobe can't get it right. PDF files exported out of Photoshop are ridiculously huge in file size, which might have something to do with it, particularly because you're rendering it at high quality print. Is the file really large? How many MB?
A workaround I use is by saving it out as a PNG then putting the PNG image into inDesign and saving it as a PDF from there. The resulting file size is about 50x smaller than the bloated PDF Photoshop puts out.