Resize PDF to 6x9, 300dpi

I already have a finished interior PDF for my book, packed with illustrations. All I need now is a clean conversion to a 6" x 9" trim size while keeping every single element at a true 300 dpi. The illustrations must stay high-resolution—no colour tweaks, background removals, or layout changes—just precise scaling and repositioning when necessary so nothing gets stretched, pixelated, or cropped.

Once you’re done, I expect a press-ready PDF that opens at exactly 6 × 9 inches, passes a standard 300 dpi pre-flight check in Acrobat, and retains the original visual quality on every page. Please send back the final PDF plus a brief note confirming the resolution test you ran.