As promised (and explained), we’re happy to announce the release of all our plug-ins for In Design CS5.5 in concert with our current CS4/CS5 releases.
When you download any of our plug-ins, and double-click the installer file in the Plug-ins for In Design CS5 folder, Adobe’s Extension Manager will install the appropriate CS5 or CS5.5 plugin, depending on your most-recently installed version of In Design.
I like Adobe products, but considering their high cost they should really include better file compatibility.) Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
The Open Asset plugin is compatible with Adobe In Design CC 2015.4 - 2018.
The best and preferred method for installing the plugin is using Adobe's Creative Cloud Add-On Store.
Download the plug-in onto your computer and if necessary, decompress it (unstuff or unzip it).
This effectively forces conversion of CS5 files to CS6 files, so that a CS6 trial user is in the position of needing to purchase CS6 in order to continue working on their CS6 files when the trial expires.
(This probably was an unfortunate marketing move on Adobe's part, because the incompatibility could cause annoyance for trial users who might therefore turn away from purchasing the latest version.
If you want to go back and forth and rely on something like IDML, just stick to features implemented in the older version.
Deviating from that rule is the only way I've seen trouble arise.