OOo expects that an encrypted document does not contain any
non-encrypted streams starting from ODF1.2 version. The exceptions are
the streams that are part of the ODF format: "mimetype",
"META-INF/manifest.xml" and signature streams that follow the pattern
In case OOo detects that there is an unexpected non-encrypted stream,
it shows the warning and let the macros in the document be deactivated.