VB.net How to Thread Procedure with Parameters

Question

I am building an application in Visual Basic Express 2008 that will iterate over rows in a datatable, generate the appropriate Word mailmerge document(s), then copy the output and paste at the end of the final output file. Everything works great in testing, but because of the mailmerge and the copy/paste procedures, it hangs the UI while it's running. It's ok for generating docs on just one file, but it takes about 10-15 seconds for one file. We will be using this tool to generate documents for hundreds of files, so it could be problematic.

The final output file must be sequential. For example, on case 1, we need to create Documents A, B, then C. Then move to case 2 and create documents A and C. Case 3 might only require document B. And so on throughout the rows of the datatable.

Seems to me I need to use threading here although I am new to the concept and having a terrible time understanding. I get the basics of it, but unsure how to apply to my program.

I have a For-Next loop to iterate over the datatable and for each row, it calls the appropriate Sub(s). Problem is the subs it calls need data from the source file. Not sure how to run this logic within a thread given the source data. Would appreciate any advice on how to set this up in a thread.

I have read all the Microsoft documentation and it makes sense if all you want to do is count from 0 to 100 or something like that.... Haven't found any examples where source data is required for the threaded process.

Here's the bit I would like to wrap up in a thread:

For i = 0 To RowCount - 1  'Iterate over the rows in the datatable

        SuitBal = SuitData.Rows(i).Field(Of Decimal)("SuitBal")

        'Only set courtstate if moving on to the next case and CourtState is not Nothing
        If Not SuitData.Rows(i).Field(Of String)("CourtState") Is Nothing _
                And SuitData.Rows(i).Field(Of Integer)("Link") = frmCreateDocsByDef.Link Then
            frmCreateDocsByDef.CourtState = SuitData.Rows(i).Field(Of String)("CourtState")
        End If

        'set next account number
        frmCreateDocsByDef.fileNum = SuitData.Rows(i).Field(Of Integer)("File")

        'Determine if this is a driver account
        frmCreateDocsByDef.IsLegalDriver = SuitData.Rows(i).Field(Of Boolean)("IsLegalDriver")

        'Determine clientshort name
        ClientShort = SuitData.Rows(i).Field(Of String)("ClientShort")

        'Determine documents and call subroutines to create and merge
        If frmCreateDocsByDef.rbILcase.Checked = True Then

            If frmCreateDocsByDef.cbGenerateAuth.Checked = True Then
                Call CreateAuth(MyApp, ASSIGN_AUTH, fileDest, OutputFileName, SavePath, "IL", "Suit", frmCreateDocsByDef.fileNum, "")
            End If

            If frmCreateDocsByDef.cbGenerateECA.Checked = True Then

                If ClientShort = "UPH" Then
                    'Initiate merge
                    Call CreateECA(UPH_ECA, fileDest, ECAfileName, SavePath, frmCreateDocsByDef.fileNum, "")
                    'Call CreateUPHECA(UPH_ECA, fileDest, ECAFileName, SavePath, fileNum, "")

                    If frmCreateDocsByDef.IsLegalDriver = True Then
                        'Call CreateUPHFAP(UPH_FAP, fileDest, ECAFileName, SavePath, fileNum, Link, "")
                        Call CreateFAP(UPH_FAP, fileDest, ECAfileName, SavePath, frmCreateDocsByDef.fileNum, frmCreateDocsByDef.Link, "")
                    End If
                ElseIf ClientShort = "HARRISBURG" Then
                    'Call CreateHarrisburgECA(HMC_ECA, fileDest, ECAFileName, SavePath, fileNum, "")
                    Call CreateECA(HMC_ECA, fileDest, ECAfileName, SavePath, frmCreateDocsByDef.fileNum, "")

                    If frmCreateDocsByDef.IsLegalDriver = True Then
                        'Call CreateHarrisburgFAP
                        Call CreateFAP(HMC_FAP, fileDest, ECAfileName, SavePath, frmCreateDocsByDef.fileNum, "")
                    End If
                End If

                'Call HMC ECA
            End If

        ElseIf frmCreateDocsByDef.rbIAcase.Checked = True Then
            If frmCreateDocsByDef.rb1Def.Checked = True Then
                'generate Verfications for 1 defendant
                If frmCreateDocsByDef.cbGenerateVfn.Checked = True And _
                    (frmCreateDocsByDef.rbAllAcctsInCase.Checked = True And frmCreateDocsByDef.IsLegalDriver = True) Or _
                    frmCreateDocsByDef.rbSingleAcct.Checked = True Then
                    Call CreateIowaVerifications(MyApp, IA_VFN_1DEF, fileDest, OutputFileName, SavePath, frmCreateDocsByDef.fileNum, "")
                End If

                'generate affidavits for 1 defendant
                If frmCreateDocsByDef.cbGenerateAffidavit.Checked = True And _
                (frmCreateDocsByDef.rbAllAcctsInCase.Checked = True And frmCreateDocsByDef.IsLegalDriver = True) Or _
                frmCreateDocsByDef.rbSingleAcct.Checked = True Then
                    Call CreateIowaAffidavits(MyApp, IA_AFFID_1DEF, fileDest, OutputFileName, SavePath, frmCreateDocsByDef.fileNum, "")
                End If

                'generate authorizations for 1 defendant
                If frmCreateDocsByDef.cbGenerateAuth.Checked = True Then
                    Call CreateAuth(MyApp, SUIT_AUTH, fileDest, OutputFileName, SavePath, "IA", "Suit", frmCreateDocsByDef.fileNum, "")
                End If

            ElseIf frmCreateDocsByDef.rb2Defs.Checked = True Then
                'generate docs for 2 defendants
            End If
        ElseIf frmCreateDocsByDef.rbWIcase.Checked = True Then
        End If

    Next

I tried creating a new Sub called "MergeDocsByDef()" with no parameters and put all this in there and then tried starting thread, but MergeDocsByDef couldn't read any of the source data from the datatable. So I added parameters to MergeDocsByDef and tried again, but then it wouldn't allow it when I changed it to Dim Th = New Thread(AddressOf MergeDocsByDef(param1, param2)).

So... if the code that I want to use in a thread iterates over a datatable and/or requires parameters, how do I use a thread? Or maybe the "real" question: How do I get the UI to not freeze up while the mail merge is taking place, while keeping the output file in order with the datatable?