The operating principle of the web is such that any content (static pages, image, etc.) is saved by a browser on local disk while displaying it. Hence, any browseable content is downloaded and saved on a disk by every browser.

This principle makes "off-line" browsers possible. They just browse the entire web site and save it on disk.

You can have all or a portion of your web site password protected. However, if the user knows the password they can browse the whole website and download it all.

The best way to protect your content is to disable Directory Browsing on /Htdocs, and on any other folders you wish to protect. This prevents people from using Windows "Web Folders" and downloading your entire site. However, there is no real way to completely protect against someone downloading the static content from your web site. They will always be able to “View Source” or “Save Target” to copy your content one page at a time.

For more information, read an article on How to Protect Your Website Content from Being Stolen.