Using any FTP client (i.e. CoreFTP), login to your web hosting account and download the HTML document you wish to password-protect.
Visit this URL and click on “Choose File” from your local download HTML document. Next enter your desired password twice and click “Submit” to continue;
After it is done encrypting your HTML file, it will automatically download it on your computer. Simply upload the same HTML by replacing the old file. Next time you (or anyone else) browse your newly created and encrypted HTML document online, you’d be asked to enter a password like this;