>>2033011From what I've gathered camping in the forested areas is generally prohibited in Austria (unless you have explicit permission of the proprietor). As for mountainous terrain (alpine Ödland), some states are more permissive than others. In Tirol, for example, camping outside of designated areas (aka camp sites in the valleys) is strictly prohibited (I would imagine all the more so in National Parks). An exception is made for unplanned emergency bivouacing (Notbiwak) i.e. when you are forced to spend the night on the mountain due to circumstances (injury, darkness, bad weather). So if you intent to bivouac beforehand it technically counts as camping and is thus illegal (if they catch you bivouacing with a camping stove you can't plead an emergency because it would be obvious that your bivouac was 'premeditated'). Although keep in mind that this the written law and I've no clue how it is enforced. Salzburg on the other hand is more lenient as long as you make a conscious effort to minimize your impact on nature.
https://www.alpenverein.at/portal/natur-umwelt/bergsport_umwelt/zelten-biwakieren.php 