Having trouble saving as PDF, colours different, fx missing

defaultv,

Obviously, your PNG is RGB.

Presumable, the PDFs are meant for print which begs for CMYK.

Which colour mode(s) are you working in (hopefully, you have the right/consistent colour management)?

Maybe far too far out, what happens if you:

1) Duplicate the Layer with the artwork,

2) Place the PNG (as link) in the duplicate Layer,

3) Transfer the basic/deepest colour in the PNG artwork to a rectangle or whatever with the Eyedropper,

4) Apply that as the basic/deepest colour in the actual artwork,

5) Make further adjustments to the colour values if needed?

As I see the basic/deepest colour, it is a sharper red in the PDFs and also darker in the copy PDF.

I shall be surprised if it proves impossible to get (much closer to) the PNG colour in PDF, regardless of colour mode.