Excel Open XML Spreadsheet Template (.xltx) represents Microsoft Excel Template that are based on the Office OpenXML file format specifications. It is used to create a standard template file that can be utilized to generate XLSX files that exhibit the same settings as specified in the XLTX file.
Learn more about this file format here
GroupDocs.Viewer (in GroupDocs.Viewer.dll) Version: 20.9
public static readonly FileType XLTX
Public Shared ReadOnly XLTX As FileType
static initonly FileType^ XLTX
static val XLTX: FileType