Call me Silly But I would love to be able to change the paper texture of Dorico to this old looking classical style paper quality…
Gorgeous… 
That’s something you can do with an exported PDF in a graphics program. You can even dither and blur the vector lines and add a bit of pen, to create something that looks exactly like the scan you started with before you typed it into Dorico.
Thanks, any suggestions for a program like that?
For a graphics program? Photoshop; Affinity Photo; Pixelmator, GIMP…
That’s to get a bitmap effect. For ‘normal’ editing of music PDFs, I’d use a vector artwork app like Illustrator, Affinity Designer, Graphic, Inkscape, etc…