How to open an Excel file in C#?

I am trying to convert some VBA code to C#. I am new to C#. Currently I am trying to open an Excel file from a folder and if it does not exist then create it. I am trying something like the following. How can I make it work?

Excel.Application objexcel;
Excel.Workbook wbexcel;
bool wbexists;
Excel.Worksheet objsht;
Excel.Range objrange;

objexcel = new Excel.Application();
if (Directory("C:\\csharp\\error report1.xls") = "")
{
    wbexcel.NewSheet();
}

else
{
    wbexcel.Open("C:\\csharp\\error report1.xls");
    objsht = ("sheet1");
}
objsht.Activate();

You need to have installed Microsoft Visual Studio Tools for Office (VSTO).

VSTO can be selected in the Visual Studio installer under Workloads > Web & Cloud > Office/SharePoint Development.

After that create a generic .NET project and add a reference to Microsoft.Office.Interop.Excel via 'Add Reference... > Assemblies' dialog.

Application excel = new Application();
Workbook wb = excel.Workbooks.Open(path);

Missing.Value is a special reflection struct for unnecessary parameters replacement

In newer versions, the assembly reference required is called Microsoft Excel 16.0 Object Library. If you do not have the latest version installed you might have Microsoft Excel 15.0 Object Library, or an older version, but it is the same process to include.

FileInfo fi = new FileInfo("C:\\test\\report.xlsx");
if(fi.Exists)
{
    System.Diagnostics.Process.Start(@"C:\test\report.xlsx");
}
else
{
    //file doesn't exist
}

private void btnChoose2_Click(object sender, EventArgs e)
{
  OpenFileDialog openfileDialog1 = new OpenFileDialog();
  if (openfileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
  {
    this.btnChoose2.Text = openfileDialog1.FileName;
    String filename = DialogResult.ToString();

    var excelApp = new Excel.Application();
    excelApp.Visible = true;
    excelApp.Workbooks.Open(btnChoose2.Text);
  }
}