Office Interop Does Not Work in Windows Service

Question

I have a very weird issue with Microsoft Office.

I have a common library whose sole purpose is to open whatever word document file type is passed to it (by a full file path...) and save that opened word document as a pdf file.

The weird issue is that if I consume that library from a windows service, whenever it attempts to open the word document, I get a null... aka, the word document never got opened.

If however I consume the library from a WPF or Windows Form application I never have any issues. I am aware that there are issues with threading, (Single Thread Appartment) however I have no idea how to fix it to work out of the windows service. :( :( :(

I would appreciate any help! The Error I get Is the following:

Exception Message: {"Object reference not set to an instance of an object."} (Referring to the word document). Inner Exception: Null; HResult: -2147467261. Data: ListDictionaryInternal with 0 entries; Stack Trace: at DocumentConverter.ToPdf(String currentWorkingFolderPath, String pathToDocumentToConvert) in c:\Project Files...\DocumentConverter.cs:line 209

So here is the library function. It requires the Microsoft Office reference, which is created by the Visual Studio Tools for Office.

private string ToPDF(string currentWorkingFolderPath, string pathToDocumentToConvert)
{
    string temporaryPdfFolderPath = Path.GetFullPath(currentWorkingFolderPath + "\\pdf\\");
    string temporaryPdfFilePath = Path.GetFullPath(temporaryPdfFolderPath + "\\pdffile.pdf");

    if (!FileSystem.CreateDirectory(temporaryPdfFolderPath))
    {
        return null;
    }

    try
    {
        Microsoft.Office.Interop.Word.Application wordApplication = new Microsoft.Office.Interop.Word.Application();

        object objectMissing = System.Reflection.Missing.Value;

        wordApplication.Visible = false;
        wordApplication.ScreenUpdating = false;

        FileInfo wordFile = new FileInfo(pathToDocumentToConvert);

        Object fileName = (Object)wordFile.FullName;

        // This is where it breaks when called from windows service. Use the dummy value as a placeholder for optional arguments
        Document wordDocument = wordApplication.Documents.Open(ref fileName, ref objectMissing,            
            true, ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing,            
            ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing,            
            ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing);



        object outputFileName = (object)temporaryPdfFilePath;
        object fileFormat = WdSaveFormat.wdFormatPDF ;

        // Save document into PDF Format
        wordDocument.SaveAs(ref outputFileName,
            ref fileFormat, ref objectMissing, ref objectMissing,
            ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing,
            ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing,
            ref objectMissing, ref objectMissing, ref objectMissing, ref objectMissing);

        // Close the Word document, but leave the Word application open.
        // doc has to be cast to type _Document so that it will find the
        // correct Close method.                
        object saveChanges = WdSaveOptions.wdDoNotSaveChanges;
        ((_Document)wordDocument).Close(ref saveChanges, ref objectMissing, ref objectMissing);

        wordDocument = null;

        // word has to be cast to type _Application so that it will find
        // the correct Quit method.
        ((Microsoft.Office.Interop.Word._Application)wordApplication).Quit(ref objectMissing, ref objectMissing, ref objectMissing);

        wordApplication = null;

    }
    catch (Exception ex)
    {
        //logging code
        return null;
    }

    return temporaryPdfFilePath;
}

Answer 1

Per @Sameer S in his post: Is Office 2003 interop supported on Windows server 2008 ..?

Officially Microsoft Office 2003 Interop is not supported on Windows server 2008 by Microsoft.

But after a lot of permutations & combinations with the code and search, we came across one solution which works for our scenario.

The solution is to plug the difference between the way Windows 2003 and 2008 maintains its folder structure, because Office Interop depends on the desktop folder for file open/save intermediately. The 2003 system houses the desktop folder under systemprofile which is absent in 2008.

So when we create this folder on 2008 under the respective hierarchy as indicated below; the office Interop is able to save the file as required. This Desktop folder is required to be created under

C:\Windows\System32\config\systemprofile

AND

C:\Windows\SysWOW64\config\systemprofile

Thanks Guys..!