I have a excel spreadsheet which is in SharePoint Web App Documents. I need to protect the sheet with password in SharePoint itself, so that it will not be public anymore. Is there any way to password protect the SharePoint excel Document?
Why not creating an excel document on your desktop + password protect it then upload it to SharePoint ?! On top of that, you can give unique permission to that specific file so that only certain users can read or edit it.
Require a password to open or modify a workbook https://support.office.com/en-us/article/Require-a-password-to-open-or-modify-a-workbook-10579f0e-b2d9-4c05-b9f8-4109a6bce643
Applying unique permission in SharePoint: https://support.office.com/en-us/article/Edit-permissions-for-a-list-or-library-02D770F3-59EB-4910-A608-5F84CC297782