You can't edit existing HTML pages using WYSIWYG Web Builder.
WYSIWYG Web Builder is not an HTML editor, but an HTML generator!
But although Web Builder is not an HTML editor, you can import existing HTML pages (version 2.1 and higher).
Select Page->Import->Import HTML Page from the menu to display the Import HTML page window. You can either select an HTML page from your local drive or specify a URL of an online website.
Click OK to start importing the page. Web Builder will automatically copy all images to your local drive (as specified in the Folders page of the Web Builder configuration).
Important notes about importing HTML:
1. WYSIWYG Web Builder is not an HTML editor, but an HTML generator! Web Builder imports the HTML by rendering the contents of an existing page and then attempts to convert the layout to Web Builder's internal object format.
2. The import feature currently only imports text, images, form elements and body attributes (link colors, background images, meta tags). Tables, scripts, stylesheets and multimedia components are not imported. But in most cases this is good enough to get you started.
3. Web Builder does not parse style sheets, so is some cases the text may look different than the original page.
4. Web Builder currently doesn't support framesets. If you want to import a web page that's using frames you'll have to import all individual pages separately.
5. It is very difficult to support all different types of HTML. Even the populair browsers will interpret HTML differently, so don't expect miracles. If a page fails to be imported it probably contains code that Web Builder doesn't understand and you still have to start from scratch.
6. Importing web pages created with WYSIWYG Web Builder will give the best results!