This is to update you on the ticket (CELLSNET-42682). Unfortunately, we will not be able to provide any means to calculate/count the number of characters in a spreadsheet due to the limitations of MS Excel specifications. Please note, the BuiltInDocumentProperties.Character property is mainly used by MS Word & PowerPoint applications.
For spreadsheets (excel files), the specification narrates as follow,
"Excel 97, Excel 2000, Excel 2002, Office Excel 2003, Office Excel 2007, and Excel 2010 omit the property, or preserve an existing value but ignore it."
As MS Excel itself either ignores the property value or omits it, therefore Aspose.Cells will not be able to get the count of characters in a spreadsheet.
Although, if you wish to accomplish this task, you have to write your own customer routines to traverse all cells & shapes in a spreadsheet to calculate the character count.
We are sorry for the inconvenience caused to you.