Do you own copyright on the PDFs? If not, I think Lulu will balk.
If it's a single copy for your own use, and if the terms of usage permit, you could just print it at home, on your printer.
The PDFs will have to be the same shape and size as the options available at Lulu, and of an allowable page count.
Note that Lulu is geared for DIY unless you wish to pay them money.
If you simply want to read them in book form, and you've paid for the PDF, prepare a private project, upload PDF, order a copy then delete the project.