David Ryeburn wrote:

In retirement, for fun and profit, I've been doing pre-publication
debugging (for publishers) of math texts written by others. When I
receive manuscripts, these are usually sent as PDF files from scans of
the actual paper pages produced by the authors.

They could well be like that to stop one reproducing them easily.

--
Dave (from the UK)

Please note my email address changes periodically to avoid spam.
It is always of the form:
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