How to automatically add *.pdf using AVOpenSaveDialogParams?

Currently I have the following piece of code.

I would only want the user to save the file as PDF with *.pdf extension.

However, with the following code, I have to input *.pdf at the end of the filename.

Is there a way to automatically add *.pdf at the end of the filename?

Your help is greatly appreciated.

AVFileFilterRec* fileFilters = NULL;    
dialogParams.size = sizeof(dialogParams);
    dialogParams.flags = kAVOpenSaveAllowAllFlag;
    dialogParams.parentWindow = NULL;
    dialogParams.windowTitle = NULL;
    dialogParams.actionButtonTitle = NULL;
    dialogParams.initialFileSys = NULL;
    dialogParams.initialPathName = NULL;
    dialogParams.initialFileName = ASTextNew();
    dialogParams.fileFilters = &fileFilters;
    dialogParams.numFileFilters = 0;
    dialogParams.settingsComputeEnabledProc = NULL;
    dialogParams.settingsExecuteProc = NULL;
    dialogParams.settingsProcData = NULL;
    dialogParams.showExportCheckbox = true;
    outDialogParams.chosenFileSys = NULL;
    outDialogParams.chosenPathName = NULL;
    outDialogParams.chosenFilterIndex = 0;
    outDialogParams.launchFile = 0;