how to load pdf from a string

I need to extract text from a pdf.
The pdf information are stored in an xml.
I can load the pdf in a string but when I try to load the pdf with the function loadfromstring I allways had an error.

I try to use setpassword before using loadfromstring but nothing change.

How to load my pdf sotred in an xml ?

thanks for your help

I use the 5.11 version under visual studio 2008 C++
sample code :
   BOOL bIsLicensing = FALSE;
  LONG lRet = -1;
    CQuickPDF* m_pQuickPDFObject = new CQuickPDF();
    if(m_pQuickPDFObject)
    {
        try
        {
            if(m_pQuickPDFObject->CreateDispatch("iSED.QuickPDF"))
            {
                bIsLicensing = m_pQuickPDFObject->UnlockKey("xxxxxx");//where xxx is remplaced by our licence
            }
        }
        catch(...)
        {
            ASSERT(FALSE);
        }

    }
        if(bIsLicensing)
        {
            lRet= m_pQuickPDFObject->LoadFromString((LPCSTR)(LPCTSTR)strPDFFromXML, strPDFFromXML.GetLength());
         }
        delete(m_pQuickPDFObject);
        m_pQuickPDFObject= 0;