To protect your HTML file from being easily edited or changed on the client-side, you can employ a few strategies. However, it’s important to note that these methods won’t provide foolproof protection since any content sent to the client’s browser can ultimately be manipulated. The goal is to make it more difficult for casual users to modify the content. Here are some tips:

1. Minification and Obfuscation:
2. Minification: Minify your HTML, CSS, and JavaScript files. This process removes unnecessary spaces, line breaks, and renames variables, making the code less human-readable.
3. Obfuscation: Obfuscate your JavaScript code to make it harder to understand. Tools like UglifyJS can help with this.
4. JavaScript Protection:
5. Use JavaScript to detect modifications: Implement checksums or hash functions on critical parts of your HTML and use JavaScript to compare them periodically. If modifications are detected, take appropriate action.
6. Disable right-click: Although it won’t provide strong protection, you can disable right-clicking to make it slightly harder for users to access browser developer tools easily.
7. Content Security Policy (CSP):
8. Implement a Content Security Policy to control which resources can be loaded and executed on your website. This can help mitigate the risk of injected scripts.
9. Server-Side Protection:
10. Most importantly, perform server-side validation and authentication for sensitive operations. Never rely solely on client-side validation or security measures.
11. User Authentication:
12. If applicable, implement user authentication to control access to certain parts of your website.

Remember that these methods provide only basic protection, and determined users can still find ways to modify client-side content. For more secure solutions, consider server-side validation and protection, especially for sensitive operations and data. Additionally, stay updated on web security best practices and technologies.