Excel exports shapes as TwoCellAnchor elements, which specifies the top left and the bottom right location of a shape. The size of the shape is recorded in the extents element (a:ext), cx and cy attributes. At the moment, the spreadsheet import first looks at the extents element and if it doesn't find the size there, calculates it from the TwoCellAnchor element. 

However, if an XLSX document has a shape with incorrect size indicated in the extents element, Excel will still be able to open it correctly, probably because it looks at the TwoCellAnchor element. RadSpreadsheet/SpreadProcessing, on the other hand, will show the image with an incorrect size.

When a csv is exported the entire range which has values is exported. When export is done in Excel, the cells of this range which are empty are marked by an additional field, separated by a comma. This comma is present in SpreadProcessing only in places where it is obligatory for example in the middle of the row. Obligatory comma in this context means that without it the file will not be read correctly by Excel or SpreadProcessing. In places where it is not obligatory, like in an empty row or in the end of the row, it is skipped. These non-obligatory commas do not influence how the file will be interpreted by Excel, however, according to the most-popular csv spec, they should be present, which means that there could be parsers which are unable to parse the resulting file. (2.4 Each line should contain the same number of fields throughout the file.) 

Example:
Exported by Excel:
---------------------------------------
Product,Unit Price,Units in Stock,Discontinued
Chai,$18.00 ,39,
Chang,,17,
Chef Anton's Cajun Seasoning,$22.00 ,53,No
,,,
Chef Anton's Gumbo Mix,$21.35 ,0,No
---------------------------------------
Exported by SpreadProcessing:
---------------------------------------
Product,Unit Price,Units in Stock,Discontinued
Chai,$18.00 ,39
Chang,,17
Chef Anton's Cajun Seasoning,$22.00 ,53,No

Chef Anton's Gumbo Mix,$21.35 ,0,No
---------------------------------------
Note the extra commas in the empty row and in the end of the first two rows in the SpreadProcessing sample.

Some of the leftmost borders are omitted when exported to PDF.

An InvalidOperationException could be thrown in multi-threaded export to XLSX format. However, the problem is not verified.

Here is the stacktrace:

ERROR System.InvalidOperationException: isParsing must be true.
   at Telerik.Windows.Documents.Spreadsheet.Utilities.Guard.ThrowExceptionIfTrue(Boolean param, String paramName)
   at Telerik.Windows.Documents.Spreadsheet.Model.Printing.HeaderFooterSectionTextParser.OnBeforeParse(String headerFooterSectionText)
   at Telerik.Windows.Documents.Spreadsheet.Model.Printing.HeaderFooterSectionTextParser.Parse(String headerFooterSectionText)
   at Telerik.Windows.Documents.Spreadsheet.Model.Printing.HeaderFooterSectionTextSanitizer.Sanitize(String sectionText)
   at Telerik.Windows.Documents.Spreadsheet.Model.Printing.HeaderFooterContent.BuildContentText()
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Model.Elements.Worksheets.HeaderFooterElement.WriteChild[T](OpenXmlChildElement`1 child, HeaderFooterContent content)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Model.Elements.Worksheets.HeaderFooterElement.WriteChildren(HeaderFooterSettings settings)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Model.Elements.Worksheets.HeaderFooterElement.OnBeforeWrite(IXlsxWorksheetExportContext context)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Model.Elements.Worksheets.WorksheetElementBase.OnBeforeWrite(IXlsxWorkbookExportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase`3.OnBeforeWrite(IOpenXmlExportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.OpenXmlPartBase.Export(IOpenXmlWriter writer, IOpenXmlExportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Export.OpenXmlExporter`2.ExportPart(OpenXmlPartBase part, TContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Export.OpenXmlExporter`2.Export(Stream output, TContext context, OpenXmlExportSettings settings)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider.ExportOverride(Workbook workbook, Stream output)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.WorkbookFormatProviderBase.Export(Workbook workbook, Stream output)

Available in LIB Version 2017.2.828.

Provide the ability to work with images in headers/footers of a worksheet. Note that large images put in headers are visualized as watermarks on printing/exporting to PDF.
Watermark in Excel: https://support.office.com/en-us/article/add-a-watermark-in-excel-a372182a-d733-484e-825c-18ddf3edf009
 

There are scenarios when the default value of the columns is changed and may be different from 65. However, RadSpreadprocessing always exports the non-custom column values as 65.

WORKAROUND: After importing the XLSX file you may make all columns to have custom values in order to preserve the column widths after the export. The following code snippet shows how this may be achieved for some Worksheet instance:

CellRange usedRange = worksheet.UsedCellRange;

for (int i = 0; i < usedRange.ColumnCount; i++)
{
    ColumnSelection column = worksheet.Columns[i];
    double width = column.GetWidth().Value.Value;
    column.SetWidth(new ColumnWidth(width, true));
}

Add support for superscript and subscript font effects for cell formatting. Currently, this is not supported by the model and is omitted on import.

When there are split panes in a workbook, the topLeftCell property can be omitted. In this case, the format provider throws NullReferenceException.

With the current implementation, references like in the following expression cannot be evaluated and are treated as strings:
=SUM('C:\Users\Your user name\Desktop\[Workbook_1.xlsx]Sheet1'!A1:B2)

Comparison operators (equal '=', not equal '<>') doesn't work as expected with references to empty cells. For example, expressions of type '=IF(A1="", TRUE, FALSE)' are evaluated to false when A1 cell is empty. 

In MS Excel, such expression is evaluated to TRUE if the cell is empty - i.e. empty cell value is considered equal to an empty string "".

Workaround: Use ISBLANK function if possible. Its results are consistent with MS Excel.

For instance, when exporting FLOOR.MATH function a #NAME error is displayed initially.

Workaround: Select the cell in Excel, click in the formula bar and press Enter without changing anything. This fixes the #NAME error and Excel manages to successfully display the function result.

The MATCH function searches for a specified item in a range of cells and returns the relative position of the item found in this range.

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/CustomFunctions

Available in R3 2017 Official Release Version

When the default number formats for Accounting and Currency are used and the current culture is Russian, the number format is not parsed correctly.

Add support for TEXT function. The TEXT function allows changing the way a number appears by applying formatting to it using format codes.

TEXT(value, format_text)

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions 

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions 
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/WPF/CustomFunctions 

Add support for CHOOSE function. CHOOSE uses the number parameter to return a value from the list of value arguments. 

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/CustomFunctions

Available in R2 2017 Official Release.

Provide the customers with the ability to export workbooks to HTML files.

Add support for TRIM function. TRIM removes all spaces from text except for single spaces between words.

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/CustomFunctions

Available in R2 2017 Official Release.

Add support for VALUE function. VALUE converts a text string that represents a number to a number.

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/WPF/CustomFunctions

This would allow repeating header rows on every printed page. More information related to this functionality may be found on the following link:

https://support.office.com/en-us/article/Print-rows-with-column-headers-on-top-of-every-page-d3550133-f6a1-4c72-ad70-5309a2e8fe8c