The fix-qdf program reads a PDF file in QDF form and writes out the same file with stream lengths, cross-reference table entries, and object stream offset tables regenerated.
For details about fix-qdf and about PDF files in QDF mode, please see the qpdf manual, which can be found in /usr/share/doc/qpdf/qpdf-manual.html or /usr/share/doc/qpdf/qpdf-manual.pdf.