Workaround: Import the document without using the default command

OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.Filter = "All Spreadsheet Files (*.txt, *.csv, *.pdf, *.xlsx)|*.txt;*.csv;*.pdf;*.xlsx|Excel Workbook (*.xlsx)|*.xlsx|CSV (Comma delimited) (*.csv)|*.csv|Text (Tab delimited) (*.txt)|*.txt|All Files (*.*)|*.*";
if (openFileDialog.ShowDialog() == true)
{
    string extension = Path.GetExtension(openFileDialog.SafeFileName);
    using (Stream input = openFileDialog.OpenFile())
    {
        Workbook workbook = WorkbookFormatProvidersManager.Import(extension, input);
        workbook.Name = openFileDialog.SafeFileName; // in the default implementation this is set after applying the document to RadSpreadsheet and triggers the event
       
        this.radSpreadsheet.Workbook = workbook;
    }
}

Currently, the InputBoxText property of the RadChat control has a read-only purpose. It is updated only when you update the text via the UI. However, the property has also a public setter which implies that it can be set, but this doesn't work. 
Allow setting the InputBoxText property, which should update the text in the input TextBox.

For the moment, you can get the RadWatermarkTextBox element using the FindChildByType<T> method and set its Text property manually.

var textBox = this.chat.FindChildByType<RadWatermarkTextBox>();
textBox.SetCurrentValue(RadWatermarkTextBox.TextProperty, "new text")

Steps to reproduce: 

1. Enter in a cell =Today()
2. Show Format Cells dialog and set Custom format "d"

Expected: The value is the day of the month.
Actual: The date is formatted as short date but has to be day of the month.

As a result, the glyphs are not measured and positioned properly. The issue applies to the TrueType and Type1 fonts.

The TableCellProperty.Padding property of the "TableNormal" StyleDefinition doesn't take effect in the UI. The same is valid for the TableProperties.CellPadding property.

To work this around, you can manually set the Padding property of all TableCell elements in the RadDocument.

 var cells = radDocument.EnumerateChildrenOfType<Telerik.Windows.Documents.Model.TableCell>();
 foreach (var cell in cells)
 {
     cell.Padding = new Padding(10);
 }