Please try the attached version. We added “FileFormatType.Excel2007Xltx” and “FileFormatType. Excel2007Xltm”.
e.g.
string fn = @"C:\ test\macrotemplate.xltm";
Workbook book = new Workbook();
book.Open(fn, FileFormatType. Excel2007Xltm); // change FileFormatType to Excel2007Xltx if opening an .xltx file
book.Save(fn, FileFormatType. Excel2007Xltm); // change FileFormatType to Excel2007Xltx if opening an .xltx file
If you do not specifies the FileFormatType, aspose.Cells for .net will auto judge the file type by the file name suffix.
e.g
string infn = path + "TEST_xltx.xltx";
string outfn = path + "TEST_xltx_out.xltx";
Workbook book = new Workbook();
book.Open(infn);
book.Save(outfn);