Document is Protected - How do I Enter Permissions Password?

i know the password , but removing protection is failing

emoveProtectionOperation removeProtectionOperation = RemoveProtectionOperation.CreateNew();

// Set operation input from a source file.
FileRef sourceFileRef = FileRef.CreateFromLocalFile(@"test.docx");
removeProtectionOperation.SetInput(sourceFileRef);

// Set the password for removing security from a PDF document.
removeProtectionOperation.SetPassword("password");

// Execute the operation.
FileRef result = removeProtectionOperation.Execute(executionContext);