I’m copying here the response from one of the forum experts. I hope you find this helpful!
“I’d recommend, in order of preference:
1. Remove and discard the covers
2. Remove and store the covers separately
3. Place sheets of thick, buffered paper between the covers and the content (e.g. 10 pt. card stock.
You don’t mention a date for the reports, but the problem plastic is likely either acetate (earlier 20th c) or polyvinyl (mid 20th c to present). Acetate gives off acetic acid (Angela here, adding that this will have a vinegar-y smell) as it deteriorates and can be strongly aggressive towards paper. Vinyl can be especially hard on text produced xerographically (plasticizers soften the resins holding the toner to the paper), but the vinyl usually needs to be in direct contact with the document for the problem to get bad.
The first edition (1993) of Mary Lynn Ritzenthaler: Preserving Archives and Manuscripts is available online full text at:
She explains the problems with plastics clearly and succinctly (p. 83 ff) although she does not address report covers explicitly.
I would hope that this collection could pursue one of the strategies above, based on how important the covers are to what they are trying to preserve.”