This is preserved in the xml once saved from MS Excel:

XlsFormatProvider: InvalidOperationException is thrown when importing a document with an unsupported BIFF record.

Workaround: Re-save the file with Excel before importing it.

The current formula: 
<c r="A1" s="1">
<f>[1]BILANS_JI!$C$2</f>
<v>22611518.026189998</v>
</c>

• Simple direct reference to a single external cell [1]BILANS_JI!$C$2
• No function, just a linked cell

The expected value to be returned is 22611518.

Add support for strikethrough font effect for cell formatting. Currently this is not supported by the model and is omitted on import.

The XlsxPartNames class expects a strict name for reading the comments parts:

public const string CommentsPartName = @"/xl/comments{0}.xml";

However, some third-party tools may change the name to GemComments.xml for example. 

MS Excel recognizes this naming for the comments part. It would be nice to provide such functionality in RadSpreadProcessing.

RadSpreadProcessing expects an integer, instead of boolean. However, according to the specification, it should be boolean:

Add support for creating Tables and applying tables styles (predefined ones or custom).

LocalizableException is thrown after removing columns from a workbook with set Print Titles.

Workaround - Remove the PrintTitles before removing the columns:

WorksheetPageSetup pageSetup = workbook.ActiveWorksheet.WorksheetPageSetup;
pageSetup.PrintTitles.RepeatedRows = null;
pageSetup.PrintTitles.RepeatedColumns = null;

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
 

Currently, the numbers in a CSV file are parsed as numbers, and the leading zeros are lost. In MS Excel, leading zeros could be preserved when the values are imported as text using the more sophisticated text import wizard (http://www.upenn.edu/computing/da/bo/webi/qna/iv_csvLeadingZeros.html ).

Workaround: The values could be extracted using a third-party (or custom) CSV parser, and inserted manually into the model, using CellSelection.SetValueAsText method (http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/working-with-cells/cell-value-types.html ).

An error occurs while importing an XLSX document with charts. Here is the stack trace:

   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Contexts.XlsxWorkbookImportContext.PairSeriesGroupsWithAxes()
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.PlotAreaElement.CopyPropertiesTo(IOpenXmlImportContext context, DocumentChart chart)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.ChartElement.CopyPropertiesTo(IOpenXmlImportContext context, DocumentChart chart)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.ChartSpaceElement.OnAfterRead(IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Read(IOpenXmlReader reader, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.ChartPart.Import(IOpenXmlReader reader, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.OpenXmlPartBase.Import(Stream stream, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.OpenXmlImporter`1.ImportPartFromArchive(ZipArchiveEntry zipEntry, PartBase part, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.OpenXmlImporter`1.Import(Stream input, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider.ImportOverride(Stream input, CancellationToken cancellationToken)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.WorkbookFormatProviderBase.Import(Stream input, Nullable`1 timeout)