How to get the PDF of a hard-to-find paper? I'm finding this paper: Adobe Camera Model.

It's the second result in Google Scholar:
the result of Google Scholar

That's it, without any linkings.

And I searched Tech. rep., Adobe, Adobe Technical Reports in Google, but get nothing useful.

I also tried the names of the authors.

What are the common methods to find the PDFs of such papers?
I see that quite a few people have cited the work. The authors of those papers can be contacted for help. I'm hopeful that they will respond kindly. 

I've experienced this before. Don't hesitate to ask them by email. But also, be ready to explain why it is needed and what you've tried to find it yourself. All the best!

Edit: The link by user 101010111100 looks like it!