Quote:
I need to export a file as a pdf for a print project, but no matter what I do, the pdf comes out with all of the colors dulled, especially the brighter ones....snip.....The image looks great as a jpg or a png, but I have no choice--I can only submit a pdf.
Very probably the PDF viewer is applying settings (or not) More generally all about colour models.
When you view the image as a jpg/png on a computer it uses RGB and for most users the computer screen brightness is set way too high.
When printed the image is converted to CMYK colour and the 'gamut' - the range of colours is less than for RGB and no boost from the computer display.
https://en.wikipedia.org/wiki/GamutRGB colors that you can see on your monitor (in particular, blue, green and all bright vibrant colors) cannot be printed and/or replicated with standard CMYK inks
You can get an idea of what a print will look like in Gimp by setting up soft proofing in Edit -> Preferences -> Color Management and View -> Color Management. (and preferably calibrate the computer display)