Is it not permissible to place anything on a paper on which a supplication (du'a) is written, and if something is placed upon it and one delays removing it, is this considered disbelief (kufr)?

A supplication (du'a) includes the remembrance of Allah Almighty and one of His names. It must be preserved and not exposed to disrespect, out of reverence for the rituals of Allah, as Allah Almighty says: "That [is so]. And whoever honors the sacred ordinances of Allah - it is best for him in the sight of his Lord." (22:30), and "That [is so]. And whoever honors the symbols of Allah - indeed, it is from the piety of hearts." (22:32). It is not appropriate to place things on top of a paper on which a supplication is written, as this constitutes a lack of due reverence. Whoever sees this should hasten to remove it. One is not judged as an infidel merely for delay or neglect unless it is done out of mockery and insult, not laziness. Everything on which the name of Allah Almighty is written must be preserved, respected, and revered.