Fixed, as in attached, and mounted (which I took kaschiert auf... as until this query!) are probably too general: two slips of cellulose-free tape on the top (back) edge of a drawing will fix or mount it on another support; but kaschiert does seem to mean bonding over the entire back surface, certainly more than by one edge (I stand to be corrected). "Paper... bonded onto card" seems a little anachronistic (though technically surely correct, if bonded taken as syn. with glued, pasted, and be it with bone glue). Leo's further entries, e.g. vb to paste (onto) or back (with) seem promising. Hence my "ans." entry here. For the Leo entries:
https://dict.leo.org/englisch-deutsch/kaschiert