It should be possible to import QIF files to Quicken and add them to accounting data, which could be then exported in QDF format. More specific information about this subject can be found at Quicken website.
Convert Quicken Interchange format to Quicken financial data.
We found 2 software records in the database related to .qif to .qdf file format conversion.
Microsoft Windows software - convert qif to qdf on Windows
A personal finance management program by Intuit
Convert from qif file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned qif to qdf. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert qif to qdf on OS X
Mac version of popular Quicken personal finance management software