Having missed the upgrades in between I now need to upgrade from CS4 to CS5 (not CS5.5 just CS5) in order to work with a particular client. Is this still possible in February 2014?
But will I be able to work with the Client's CS5 files if I pay for a CC subscription? And when I pay this month and don't need the CC facility for the next 6 months can I stop paying and then start again when I need it?
For the most part newer versions of Photoshop are backwards compatible with older versions of Photoshop. However there are exceptions sometime UI and features are removed so sometime a few older assets are not compatible. Also if you work one these older assets and make updates. If you give you client you updated files they may not be able to process all the update. Older versions can not be forward compatible with newer versions of Photoshop support for newer features does not exists. If you save PSD using the maximum compatibility option in the newer version of Photoshop layers that you used newer features on may be able to be rastersized by to older version of Photoshop during Photoshop open file process.