With pdfcpu v0.8.0 (tested on Windows and Linux), bookmarks that contain CJK characters often get garbled after encryption.
For example, the attached in.pdf contains a single bookmark, "质量" ("quality" in English). out.pdf is generated with:
pdfcpu encrypt -opw myopw in.pdf out.pdf
, and the bookmark text becomes "赜⢑케" (unreadable even in Chinese). It doesn't change after decryption.
in.pdf
out.pdf