git: add uncompressed pdf file

I think I have one of the rare cases where I want to add a PDF file into a git repository.
In fact I have two cases:

• I have no source PDF
• I do have a source but I need the created PDF in a testcase.

Of course, this is expensive.
Now I think about adding the file uncompressed.
That way I can diff.
Although the initial version is expensive,
I think not more expensive than if compressed,
as far as I understand, further versions are less expensive,
because the PDF changes only in detail, mostly textual.

My question is twofold:

• does my idea make sense?
• if so, how can I make git uncompress when checking in
  and compress again when checking out?

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