Files with .XLT extension are template files created with Microsoft Excel which is a spreadsheet application which comes as part of Microsoft Office suite. Microsoft Office 97-2003 supported creating new XLT files as well as opening these.
Learn more about this file format here
GroupDocs.Conversion (in GroupDocs.Conversion.dll) Version: 188.8.131.52 (20.12)
public static readonly SpreadsheetFileType Xlt
Public Shared ReadOnly Xlt As SpreadsheetFileType
static initonly SpreadsheetFileType^ Xlt
static val Xlt: SpreadsheetFileType