Regression from commit 78e25558e8
(tdf#106059 PDF export: create a reference XObject for JPG images with
PDF data, 2017-02-23), once a PDF image was inserted to a document, an
encrypted PDF export lost those images.
The reason for this is that we started to preserve PDF images as vector
data with the above commit, but this means we copied over PDF objects
from PDF images to the export result as-is, so encryption was not
performed for them.
Fix this by separating the write of the PDF object headers, stream
content and object footer and then calling
checkAndEnableStreamEncryption() / disableStreamEncryption() for each
object, even if it's not something our PDF export created but comes from
a PDF image.
Note that when existing PDF files are signed, PDF objects are also
copied into a vcl::filter::PDFDocument, but such PDF images are never
encrypted, so it's fine to have stub implementations in
vcl::filter::PDFDocument.
Change-Id: I2f74b9f51cd35b4319221532ca890e197bab9cf3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/137242
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
