I would think there should be some third-party software to convert (or rather format) WikiPedia output to the file-type of your choice, such as a Word file, but I'm not finding anything while searching right now. Mostly because if you use the word WikiPedia in Google, you'll get mostly WikiPredia content.
I do mean something that would read the Wiki markup itself, not the HTML representation, which is itself rendered from the Wiki markup.
If you want to preserve the formatting while keeping the file as HTML, without any special tools or software, then you can open it in a standard text editor like Notepad.
You should be able to delete sections/portions easily by following one basic rule.
Always make sure that any HTML tags are either kept or removed as a matching pair.You don't really need to know what the tags do to make simple edits such as removing text.
What this means is that when deleting content, either do not touch HTML tags when cutting out text between them, or make sure you remove them in pairs when deleting longer portions of the file.
Tags are similar to the ones used here on the BBS, but using pointy braces < > instead. A closing tag includes a slash before the tag identifier. For example, the paragraph tag <p> and its closing tag, </p>
If you see a whole paragraph you want to remove, it should be totally safe to remove from the open tag to the closing tag without altering the remaining formatting.