How to convert Legacy XLS 97–03 Spreadsheet to Excel XLSX in C# .NET Framework

Updating from legacy XLS format to the current XLSX format can be both crucial and pain-saving, whether it’s for an app or client. That said, the actual process of converting between these file formats is a whole mess unto itself for anyone using C#. Luckily for you, we’ve already taken care of this for you and packaged it into an API that’s ready to go.

To use the API we are going to first install the client; copy this command into your Package Manager console, and NuGet will take care of this for us.

Install-Package Cloudmersive.APIClient.NET.DocumentAndDataConvert -Version 2.2.0

OK, now call the API function ConvertDocumentXlsToXlsx, like this:

using System;
using System.Diagnostics;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Api;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Client;
using Cloudmersive.APIClient.NET.DocumentAndDataConvert.Model;
namespace Example
{
public class ConvertDocumentXlsToXlsxExample
{
public void main()
{
// Configure API key authorization: Apikey
Configuration.Default.AddApiKey("Apikey", "YOUR_API_KEY");
// Uncomment below to setup prefix (e.g. Bearer) for API key, if needed
// Configuration.Default.AddApiKeyPrefix("Apikey", "Bearer");
var apiInstance = new ConvertDocumentApi();
var inputFile = new System.IO.Stream(); // System.IO.Stream | Input file to perform the operation on.
try
{
// Convert Excel XLS (97-03) Spreadsheet to XLSX
byte[] result = apiInstance.ConvertDocumentXlsToXlsx(inputFile);
Debug.WriteLine(result);
}
catch (Exception e)
{
Debug.Print("Exception when calling ConvertDocumentApi.ConvertDocumentXlsToXlsx: " + e.Message );
}
}
}
}

Alright, we’re already done. Pretty easy, right?