Yes, it would be a disaster as a preservation technique.
It seems you consider these valuable objects. If you want them to retain their value, you should find a reversible preservation technique.
Self-adhesive plastic will basically glue itself to the paper, and removing these films will definitely cause damage (tearing fibres from the paper, removing the ink, possibly infusing the paper with chemicals that will deteriorate it).
The best option for the longevity and preservation of these items is to bring them to a conservator.
If that is no option, you can find other methods and points of attention among our list of questions (for example here).