Package documents do not fit on package?

I have two documents (customs certificate and shipping label) that I need to attach to a package (DHL) that's being sent abroad. However, both documents together won't fit on the front of the package.

Both documents MUST be there, both are actually provided as PDFs by the greetings.

Do I now stick one on the front and the other on the back?

The package has approximately dimensions of 40x20x15.

Or should I print the shipping label smaller? That seems risky to me, given the important barcode.

Thanks in advance!