PDFLib: Set the PDF Version in the file

Hi,
I have a problem when I try to setting the version of the PDF saved.
I try to use the method PDDocSaveWithParams, in the PDDocSaveParamsRec I set the two values "minor" and "major", respectively the minor PDF version number and the major PDF version number of the document, but these values are ignored in the saving process. The file is saved with minor = 1 and major = 6 ("major" corresponding to the "%PDF-1.6" at the first line of file create, right?).
I try to save a blank page or a populated page: same result.
I try to use the methods PDDocGetVersion and PDDocSetMinorVersion for modify the pdDoc object before the file-saving. Same result: the minor value don't change: minor = 1 before and after the PDDocSetMinorVersion method. I try to put in many values 2-3-4-5-6-7... no results.
What I did wrong? Please help.

Thanks,
Pasquale