Linux doesn't really know about drives, it knows about partitions and mount points.
Obviously this is a simplification, but in general it's close enough. It also could well be your problem - timeshift doesn't know or care that /boot is on the same physical drive as the rest of your system: if it's a different partition, it's separate.
You can easily report if you're using kbin website, don't know how it works if you're using an app. You just hover over the "more" link and a dropdown appears with "Report" as the first option.
Not really a viable solution for many scenarios though. What if your PDF has half a dozen pages, your answer becomes really tedious. And in a lot of cases a PDF with forms is expected to be sent back to the person or company that created it once the fields have been filled in. They're not likely to want to receive a bunch of JPEG screenshots instead.