There isn't really anything special about header or footer text. To recognise it, Acrobat needs extra information. That would be metadata, which if I understand correctly, you removed.
I don't understand. Are you saying that Acrobat doesn't store header and footer text in a very simple data format, but that it's existence is somehow tied in a co-dependent way to (what I think some would agree is really unimportant) metadata? That principle, to me, is akin to a car being stripped down to it's chassis, and then being unable to get from A to B self-propelled because it is has had of all of it's comfort/safety/aerodynamic elements removed. Also, if Acrobat cannot recognise the header and footer text, how can it even display it?
A typical PDF (not a rarer "tagged") PDF has a completely flat structure. There are paragraphs, columns, page numbers, captions, titles, headers, footers, footnotes. There is no marker of any kind for any of them, just fonts, sizes, positions on the page.
Acrobat has no need to know "this is a footer" or "that is a subtitle" - just the font, size and position.
When you add footers and headers with Acrobat, for your convenience, it makes a note that says "this text is a header/footer". This note is not part of the visible page, and is therefore, I would say, metadata. While some people think of metadata as just author, title, keywords, it is in fact any supplementary info about the file.
So, if you remove the metadata, you can expect these convenience markers to be lost. You have a paradox: you are saying metadata is unimportant and deleting it, then complaining that the metadata you removed was, in fact, important.
Then why does Acrobat allow you to Add, Update or Remove specifically "Header" and "Footer" content. Why is this not considered just an element of the main document, and as such creatable, updateable, and removable just like any other text box, object, etc.
Yes, to me metadata is any data that doesn't directly relate to the display of content, or visible content itself. Hence, the type of the content is not metadata, but all the authors, editing time, current/previous storage locations, etc, is.
Discussion on what is and what is not considered metadata aside, I am sure there are a number of others that also don't expect that removing metadata would affect any content of the main document. My prior held belief as to the reason for the functionality is to remove the aforementioned information that is more likely to be sensitive (in the privacy sense) than that which is deemed acceptable to share in the visible content of the main document.
Can you suggest a use case for removing what Acrobat considers metadata?
It doesn't affect the content, or its editability, so far as I can see from your description. It affects only the one function: automatic removal.
I don't understand what you mean by a use case. If something is metadata and you ask to remove it, to leave it behind would surely be a fault. You seemingly don't want this information about content (metadata as it is usually called) to be metadata, or perhaps you want "remove all metadata except the metadata allowing me to remove headers". But that wasn't the design. If you want to make a feature request for such an option or behaviour, you can make a case for it, but in this forum it's more about how things are than how they might be.
By use case I mean as well as removing the sensitive hidden information, why would a user also want (at least) a header or footer they explicitly setup to be different from the rest of the document contents being turned into (what I believe is, as I haven't got ready access to Acrobat to test this) either A) A regular document element, or B) A part of the background of the page, as I am starting to get the idea that removing metadata should probably at least use the term "flatten" in the steps used to perform this operation.
As to the discussion about what is and isn't metadata, I decided to actually lookup what authorities on words consider "metadata" to mean. Oxford dictionaries defines it as "A set of data that describes and gives information about other data." (www.oxforddictionaries.com/us/definition/american_english/metadata). This to me doesn't mean it defines the data, just it is ancillary data that supplements other data/explains why it exists, how it came to exist, when it came to exist. If metadata is to include whether something is different from something else, then to me this should also include fonts, sizes, colours, and even positions on a page.
To address your 'discussion ended, because my problem has been identified as actually a feature, i.e., expected behaviour' - The line between feature and bug is not exactly clear, and I don't personally see the harm in discussing what isn't, so long as both parties don't mind and have something to constructively contribute to their point(s).
Lastly, as I was writing this I heard back from the user. Is it correct that using the Update and Remove options spoke about in my initial question, without any metadata removal operation being prior performed on the document, both remove the existing header & footer?
If removing metadata removes the visible header or footer, changing the appearance of the page, that is a bug. It is not the assumption on which I have been answering.
My assumption is that it reflects the users ability to later remove the header or footer that was added. This I deduce from your symptoms: either "Update" or "Remove", leads to dialog boxes being displayed stating "Acrobat cannot find any headers or footers in this file, which does not to me say the headers or footers are gone.
Clearly if the user wants to remove metadata and remove headers/footers they need to do it in the opposite order.
I never suggested that removing metadata would remove the header or footer. I was asking what state the header and footer are left in, and what state other document elements that Acrobat thinks need "convenience" markers, are left in, post metadata removal.
The text you quoted is not part of the symptoms of the original question. It is a separate and distinct question.
Your input into this subject is not helping. You do not appear interested in providing direct answers to my questions (rather trying to draw my words into your tunnel vision), nor exploring the issue, but rather tunneling this subject into "this is the way it is. there is no workarounds. live with it". I realised this morning that you have not even thought it helpful to find and provide a list of elements that Acrobat considers metadata. As this seems to be at a crux of our conversation, I have done a search for this now, and surprisingly many others seem to have the same opinion on what is/isn't metadata as I (Search the following pages for any mention of "header" or "footer"). Please see below links if you are interested, but regardless I request that you not try and provide further help and leave this question up to provide others the opportunity to provide their input, whenever that may happen.
P.S Adobe forum designers - Highlighting content in the text box used to write this, and selecting formatting controls perform the requested operation on the selected text. Doing the same with something to hyperlink provides a popup box that doesn't even have the URL pre-populated. Take a cue from gmail's book, please
I'm sorry if I'm not being helpful. I see your problem as an unwillingness to accept the design and implementation of PDF, and I was trying to get you to recognise this. I will shut up now. I had not realised that there was more than one question. You might like to restate them for the benefit of others.