passing documents through pages

I am wondering what people's opinions are for the following.

I am storing a library of documents online (the directly viewable ones will be in HTML format - with other formats for the user to choose if they wish to download them).

Anyway -
I have main site with PHP scripts taking user selection and then providing the document for reading.
Since the documents are all stand alone html I want them to be viewed in the website - ie. I want the sites menu, banner, and footer displayed around the document.

Currently they are simply being read into the site's page but this is wrong since this means CSS definitions are being loaded inside the page body (not in the header).

I would like to keep the documents stand alone but also bring them in.
What would be the simplest method to load the document in?

I thought of iframes but I dislike that method. I could place the needed CSS definitions in the site's page but then if viewed alone the documents would not look right.

Like I said - any opinions?

If it is to complicated then I may just re-adjust the plan and force them to be viewed through the site's pages only.

Thanks
Mike

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