SOLVED: Problem with Impressive

I've written before (here and here) about using the open-source Impressive program to display PDF presentations. It's been quite a while since I used it, or any other presentation software for that matter -- retired geezers don't do a lot of presenting -- but I'll be helping the INFORMS Student Chapter at the University of Louisville catch up on their sleep this coming week, so I thought it was time to install something on my laptop. A quick Google search revealed that not much has come down the pike in recent years to rival it, so I installed Impressive. The version in the Canonical repositories is a bit dated, so I got the current version from Liviu Andronic's PPA. (Thanks, Liviu, for maintaining this!)

Impressive (and various dependencies) installed just fine, but when I tried to open one of my slide shows, I got the following error:

Warning: The input file `<path to my file>' could not be analyzed.
The presentation doesn't have any pages, quitting.

So I tried opening a random PDF I had lying around my laptop's desktop screen, and lo and behold it opened! After banging on Google and finding mostly rather antiquated posts, the most plausible explanation I could find was something about graphics being produced in a "recent" (several years ago) version of PDF and the current (back then) version of the PDFtk toolkit (pdftk) having a bug, with the suggested fix being to revert to an older version of pdftk. I looked in the Synaptic package manager to see what version I had, and it turned out the answer was none!

I installed pdftk (and necessary dependencies) from the Canonical repositories, and that fixed the problem. Impressive now worked just fine with my presentation. This leaves me with a few observations:

• Neither pdftk nor any of the dependencies that installed with it must be absolute dependencies of Impressive, since Impressive was able to display the second file I tried without having pdftk etc. installed.
• The pdftk bug mentioned in the old posts has, I'm pretty sure, long since been fixed ... and, in any case, that wasn't the problem, since I did not have any version of pdftk, buggy or not, installed.
• Either pdftk or one of its dependencies, while not strictly required to run Impressive, must be required to correctly parse something (all graphics? some graphics? something to do with the use of overlays?) in my presentation.

Bottom line: I don't fully understand what happened, but at least it works now.