A Parable (For your client)
I was once given the opportunity of engineering non-copyable literature for distribution.
The stipulation was that the original time-sensitive document could be read by the private seminar participant but would be difficult or impossible to reproduce conveniently until the information became stale. It was to be a limited edition.
I tried several different concepts. The most successful attempt was made on paper stock that was difficult to reproduce due to a light multi-coloured interference pattern on the paper that when copied became darker. The dots used were non resolvable by the normal copiers and became continuous multicoloured blocks. The lithography overprinted human-readable characters were also halftone screened but neutral that could be seen and read.
Office photocopies of the original pages were a blotchy difficult to read mess. Colour photocopies were a colourful blotchy difficult to read mess.
So far, so good. Proof of concept, check. We went into production.
Everything worked as designed and it only took minutes to crack. It was dictated to a speed typist who then had a second perfect original to copy in a few minutes.
Moral: If you have an original, there will be a way to reproduce it.
Another alternative approach would be to create a way so that the recipient wouldn't want or allow a copy of it. For example: Use a watermark of the recipient's credit card number and the PDF will be very carefully tended. There are more ways, too.