Hello,
We have exactly the same problem. We've used the DIN font for a few yars now, without any problem, and since Adobe Reader was last updated, none of our pdf documents can be read anymore.
It seems it's not a problem coming from the documents, but a problem coming from the new Adobe...
All our documents (old or new) seems to be without text, whoever tries to read them (us, client, partners, etc)
I'm looking for a solution too !