I don’t think you can move PDF pages outside of a file, only within the file. I would use a PDF editor on my computer to combine them. They generally cost money, but maybe there are free ones? Adobe Acrobat comes with Creative Cloud if you have that. I’ve used https://www.pdf-xchange.com/product/pdf-xchange-editor for years, but it looks more expensive now. There are probably online tools that could do it if you don’t mind copying the files on a website. Or we could ask rmhacks to add this to his RCU utility.