using IronXL;

WorkBook workBook = WorkBook.Load("sample.xlsx");
WorkSheet workSheet = workBook.DefaultWorkSheet;

// Open protected spreadsheet file
WorkBook protectedWorkBook = WorkBook.Load("sample.xlsx", "IronSoftware");

// Spreadsheet protection
// Set protection for spreadsheet file
workBook.Encrypt("IronSoftware");

// Remove protection for spreadsheet file. Original password is required.
workBook.Password = null;

// Worksheet protection
// Set protection for individual worksheet
workSheet.ProtectSheet("IronXL");

// Remove protection for particular worksheet. It works without password!
workSheet.UnprotectSheet();

workBook.Save();

Imports IronXL

Private workBook As WorkBook = WorkBook.Load("sample.xlsx")
Private workSheet As WorkSheet = workBook.DefaultWorkSheet

' Open protected spreadsheet file
Private protectedWorkBook As WorkBook = WorkBook.Load("sample.xlsx", "IronSoftware")

' Spreadsheet protection
' Set protection for spreadsheet file
workBook.Encrypt("IronSoftware")

' Remove protection for spreadsheet file. Original password is required.
workBook.Password = Nothing

' Worksheet protection
' Set protection for individual worksheet
workSheet.ProtectSheet("IronXL")

' Remove protection for particular worksheet. It works without password!
workSheet.UnprotectSheet()

workBook.Save()