How to password protect an Excel file in C#
Introduction
This C# recipe shows how you can open an unprotected Excel file and save it as a new password protected Excel file
Ingredients
The recipe uses the EPPlus library version 4.5.3.3. This is the last version of EPPlus under the LGPL License (aka free for commercial uses). You can install it using Nuget Package manager:
Install-Package EPPlus -Version 4.5.3.3
C# Code
var unprotectedFile = @"C:\Temp\ExcelRecipes\Password\unprotected.xlsx";
var protectedFile = @"C:\Temp\ExcelRecipes\Password\protected.xlsx";
// open protected file
using ExcelPackage fileExcelFile = new ExcelPackage(new FileInfo(unprotectedFile), "");
// save as unprotected file
fileExcelFile.SaveAs(new FileInfo(protectedFile), "secret123");