A subset of HTML + CSS (+ ECMAScript?) could replace PDF for this purpose. However, is there a standard subset and familiar, understandable tools for working with it? In general, using the 'save as' function in a web browser won't produce a document that looks the same 10 years later. Rewriting the source document using a tool like wget can achieve this, but it doesn't always work (eg. what if the content was pulled in asynchronously?), and you need a computer expert to create and explain how the archived format relates to the live content. 'Save as PDF,' despite its technical inferiority, is easy and widely understood.