2011-05-07.

PDF files can have true 'protection', by being encrypted and needing a serious 
password to permit decryption; this way one wouldn't be able to do anything with 
them unless having the password or a very very long time (and luck) of cracking
the code (unless something's badly implemented -- I haven't checked for the 
history of pdf security, since I'm not interested in using such features anyway,
but would put the whole file into GPG or the like if I cared).

But there's another level of 'protection' which is infuriating in its time-wasting
and pettiness:  the need of a password to split or join or print or whatever, in 
spite of being able to view.  This is not something hard, but just that the reader
is honouring a request set by the file that a password should be given for such 
operations.

It's particularly annoying that even Free Software programs such as kpdf and pdftk 
appear to follow such specifications (because the pdf specification says that 
readers should); kpdf at least has an option "Obey DRM restrictions" (in KDE 3.5), 
that can be turned off, but pdftk doesn't that I've found.

It is of course easy to turn off such behaviour before compiling.
As of pdftk-1.44 the relevant file is:
./pdftk-1.44-dist/java/com/lowagie/text/pdf/PdfReader.java
and the line (#109) is:
    protected boolean passwordIsOwner= false; // added by ssteward
which clearly should be corrected to...
    protected boolean passwordIsOwner= true;


Then compile, and run without hindrance.
On Gentoo it needs:
ebuild /usr/portage/app-text/pdftk/pdftk-1.44.ebuild unpack
vi /tmp/portage/app-text/pdftk-1.44/work/pdftk-1.44-dist/java/com/lowagie/text/pdf/PdfReader.java
ebuild /usr/portage/app-text/pdftk/pdftk-1.44.ebuild compile
ebuild /usr/portage/app-text/pdftk/pdftk-1.44.ebuild install
ebuild /usr/portage/app-text/pdftk/pdftk-1.44.ebuild qmerge


Then pdftk will naturally ignore any ignorable restrictions (i.e. other than 
a truly encrypted file input without password).  
The simplest form of restriction removal is:

$ pdftk in.pdf cat output out.pdf


$ pdfinfo in.pdf | grep ^Encryp
 Encrypted:      yes (print:yes copy:no change:no addNotes:no)

$ pdfinfo out.pdf | grep ^Encryp
Encrypted:      no