> Hi,
> load for update (and using WriteUpdate()) means that you keep the file
> as is and only add your changes at the end. Having new values encrypted
> and old values not, or using different encryption method, or even
> trying to use old encryption on the new content, doesn't sound right to
> me.
Ok, that explains my 1.) and the side note.
> It’s not technically possible to sign an encrypted PDF – because there is
no way to encrypt the new update section
> with the same key as the previous sections – unless you know what it is
(and then it’s a bit tricky still).
Convinced me ^^.
Some follow-up questions I'd like to ask:
- For my case 2.), signing an encrypted pdf with normal loading, I
learned that the resulting pdf seems to have no password at all.
How does this happen? Does podofo remove the password encryption
automatically when writing the signed file or is this some kind of error in
the viewer?
- Instead of adding the encrypted pdf as attachment, which is a nice
idea I didn't think about, would it work to append the pages of the
encrypted pdf to an empty pdf and set encryption and signature then? I know
there's an issue with embedded files when appending, but I could extract
the files and delete them prior to appending and add them later again.
- I had a third question, but I don't know what it was about anymore :-/.
Regards,
F.E.
2017-08-02 0:45 GMT+02:00 Leonard Rosenthol via Podofo-users <
podofo-users@lists.sourceforge.net>:
> It’s not technically possible to sign an encrypted PDF – because there is
> no way to encrypt the new update section with the same key as the previous
> sections – unless you know what it is (and then it’s a bit tricky still).
>
> Better to simply create a new PDF with the encrypted PDF as an attachment
> as part of a collection and then sign the new PDF.
>
> Leonard
>
> On 8/1/17, 11:27 AM, "zyx" <z...@litepdf.cz> wrote:
>
> On Tue, 2017-08-01 at 16:38 +0200, F. E. wrote:
> > As a side note, I noticed that I cannot use load-for-update in this
> > case, because the resulting pdf has an unknown password protection.
> > Neither my specified user nor owner password work for decryption.
> > That's odd and mighht be a bug, don't know ...
>
> Hi,
> load for update (and using WriteUpdate()) means that you keep the file
> as is and only add your changes at the end. Having new values encrypted
> and old values not, or using different encryption method, or even
> trying to use old encryption on the new content, doesn't sound right to
> me.
>
> Doing sign & encrypt at the same time sounds the way to go, as you
> figured out yourself.
> Bye,
> zyx
>
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