Download (free) Pdf Architect,
go to https://editor.cutepdf.com/edit.asp and put in the amout of pages that your reader is off in the beginning of the document. Do it so that your pages now have the right numbers. Let's say that my first page is page 13. I put in 12 blank pages at the beginning of the document.
Download your file now with the extra pages in the beginning of your document.
Open the document in adobe reader. Press print. Select the pdf-Creator printer and select to print page from the first real page (that is not the extra blank page that you have put in). In my document that would be from page 13.
Now you press print and Pdf Architect will pop up, and you can save it. When you then open the saved file you will see, that the first page has another number, in my case 13, next page 14 and so on.