The TXTextControl.DocumentServer.MailMerge class provides an extensible framework to inject custom logic to the merge process. The TXTextControl.DocumentServer.MailMerge.FieldMerged event can be used to manipulate the results, but also gives access to the surrounding instance of the TXTextControl.TableCell class.

This combination allows creative implementations such as conditional table cell colors based on specific filter instructions.

In the following sample, the table cell Qty should be highlighted red, if quantity is higher than 10, otherwise it should be green.

These conditions can be adjusted in the following dialog:

When merging the document, the conditions are evaluated in the custom events:

The class CellFilterInstructions contains the instructions for the custom filter:

public class CellFilterInstructions
{
  public double? CompareValue { get; set; } = null;
  public RelationalOperator? Operator { get; set; } = null;
  public Color TrueColor { get; set; } = Color.White;
  public Color FalseColor { get; set; } = Color.White;

  public enum RelationalOperator
  {
      Equals = 0,
      NotEqual,
      LessThan,
      GreaterThan,
  }
}

This class is serialized as JSON and stored in the TXTextControl.TableCell.Name property. When a new dialog is opened, the JSON is deserialized and passed to the dialog. After changes are made, the object is stored as a serialized JSON string back in the TableCell.Name property.

// create a new dialog form
frmCellFormat frmCellFormat = new frmCellFormat();

// check, if there are existing filter instructions
CellFilterInstructions cellFilterInstructions = 
    (CellFilterInstructions)JsonConvert.DeserializeObject(
        textControl1.Tables.GetItem().Cells.GetItem().Name, 
        typeof(CellFilterInstructions));

if (cellFilterInstructions == null)
{
    // create new instructions
    Color cCellBackColor = textControl1.Tables.GetItem().Cells.GetItem().CellFormat.BackColor;

    cellFilterInstructions = new CellFilterInstructions()
    {
        TrueColor = cCellBackColor,
        FalseColor = cCellBackColor
    };
}

// show the form
frmCellFormat.CellFilterInstructions = cellFilterInstructions;

if (frmCellFormat.ShowDialog() == DialogResult.OK)
{
    // save the instructions in the Name property
    textControl1.Tables.GetItem().Cells.GetItem().Name =
        JsonConvert.SerializeObject(frmCellFormat.CellFilterInstructions); 
}

In the FieldMerging event, the instructions are evaluated and the custom background color is applied to the cell that is returned in the event arguments:

private void MailMerge_FieldMerged(object sender, 
                                   TXTextControl.DocumentServer.MailMerge.FieldMergedEventArgs e)
{
    // custom field handling
    if (e.TableCell == null)
        return;

    // if TableCell.Name has instructions, create a CellFilterInstructions object
    // and evaluate the instructions and set the table cell color
    if (e.TableCell.Name != "")
    {
        CellFilterInstructions instructions = 
            (CellFilterInstructions)JsonConvert.DeserializeObject(
                e.TableCell.Name,
                typeof(CellFilterInstructions));

        // retrieve the color
        Color? color = instructions.GetColor(e.MailMergeFieldAdapter.ApplicationField.Text);

        // apply the color
        if(color != null)
            e.TableCell.CellFormat.BackColor = (Color)color;
    }
}

Test this sample on your own and download the GitHub repository.