If I simply import the xls file with the XlsFormatProvider that RadSpreadProcessing offers and then export it either to xls or xlsx format, the following message pops up when opening the document in MS Excel:

The exported XLS or XLSX file with RadSpreadProcessing contains an additional <definedName>: 

<?xml version="1.0" encoding="utf-8"?>
<workbook xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships" xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
	<sheets>
		<sheet sheetId="1" name="Sheet1" state="visible" r:id="rId1" />
	</sheets>
	<definedNames>
		<definedName name="Print_Titles" localSheetId="0" hidden="false">Sheet1!$A$1:$IV$3</definedName>
		<definedName name="_xlnm.Print_Area" localSheetId="0" hidden="false">Sheet1!$A:$G</definedName>
		<definedName name="_xlnm.Print_Titles" localSheetId="0" hidden="false">Sheet1!$1:$3</definedName>
	</definedNames>
</workbook>

ArgumentNullException is thrown when importing a document containing a rule with no set format.

It would be beneficial for the clients if every cell has this "cached value" even if the formula can't be evaluated for some reason with the SpreadProcessing - no need for recalculation, just reading the value. It should read the last values while the document was being saved at the originator.

Getting a method like "GetCachedValueString ..." , ideal with the same formatting used for the cell and localization, would be helpful. 

Incorrect calculation of UsedCellRange when conditional formatting is applied to a large cell range.

Workaround:

var usedCellRange = workbook.ActiveWorksheet.GetUsedCellRange(
    CellPropertyDefinitions.AllPropertyDefinitions
    .Except(
        CellPropertyDefinitions.AllPropertyDefinitions.Where(p => p.Name == "DataValidationRule" || p.Name == "ConditionalFormatting")));

ArgumentException  at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Theme.SystemColorElement.GetColor(IOpenXmlImportContext context)

The problematic value is val="windowText"

When an xlsm file is imported and then exported, a new ThisWorkbook object is created in the VBA browser. This creates issues when making VBA functions that have to be executed upon opening of the file.