Following example shows how to convert between XLS, XLSX, ODS, CSV and HTML files by using only the GemBox.Spreadsheet .NET component.

GemBox.Spreadsheet is a C# / VB.NET component that provides a simple and efficient way to read, write, convert, and print native Microsoft Excel (XLSX, XLS) and other spreadsheet (ODS, CSV) formats and various document formats (HTML, PDF, XPS) from .NET applications without the need for Microsoft Excel on either the developer or client machines.
GemBox.Spreadsheet Free is free of charge, while GemBox.Spreadsheet Professional is a commercial version that is licensed per developer.
For more information, see GemBox.Spreadsheet Features or try our examples.

Example loads input file from specified input format (XLS, XLSX, ODS, CSV or HTML) and saves it to output file in specified output format (XLS, XLSX, CSV, ODS, HTML, PDF, XPS or image):

C# code:

// Load Workbook from XLSX, XLS, ODS, CSV or HTML format
// and save it to XLSX, XLS, ODS, CSV, HTML, PDF, XPS or image (PNG, JPG, etc.).
ExcelFile.
Load(Path.ChangeExtension("Workbook", inputFileFormat)).
Save(Path.ChangeExtension("Workbook", outputFileFormat));

Visual Basic .NET code:

' Load Workbook from XLSX, XLS, ODS, CSV or HTML format
' and save it to XLSX, XLS, ODS, CSV, HTML, PDF, XPS or image (PNG, JPG, etc.).
ExcelFile.
Load(Path.ChangeExtension("Workbook", inputFileFormat)).
Save(Path.ChangeExtension("Workbook", outputFileFormat))