The requirement is strange. 1.7 is the final version of Acrobat, hardly a minimum. But more to the point, every PDF 1.3 and PDF 1.6 file is automatically a PDF 1.7 file. PDF 1.7 isn't a new thing, it just adds some options. Worst of all, Acrobat will automatically use the LOWEST possible PDF version, to keep compatible. You can try the PDF optimizer in Acrobat Pro, worth a try. If not sure where it is, let us know your Acrobat Pro version. Personally I'd ignore the requirement and see what happened.