The PDF file format includes a number of protection flags which specify whether the reader is allowed to print the file, make changes, or to copy out excerpts. There is nothing in the format which actively prevents such activities; these flags are simply instructions which any application operating on PDF files is expected to observe. If the "no copy" flag is set, cutting and pasting text from the file should - by the standard - be disabled in any reader application. Developers of free applications have, as a general rule, never quite gotten around to implementing this kind of restriction - even though the low-level poppler PDF-processing library makes such support possible. Applications which do implement this "feature" tend to disable it by default.

This is not the case with Okular, though. An attempt to select text from a suitably-marked PDF file yields a rather confusing dialog which reads "copy forbidden by DRM" (see the image to the right). Amusingly, the application will still allow the selected region to be saved as an image file, but sending the text to the clipboard is not allowed. There is a configuration option which disables this behavior, but the default setting is to enforce the copy restriction flag.

John Goerzen encountered this behavior in Debian's Okular package; suffice to say he was not pleased. He filed a bug and asked:

One of the important roles played by distributors is to serve as an intermediary between upstream projects and their users. If a development project does something which is not in the interests of its users, distributors have the opportunity, thanks to free licensing, to fix the problem. A look at a typical distributor's source packages will reveal that a number of applications have been patched in ways which change their behavior and generally make them fit in better. This final bit of finish is part of the value that distributors add.

Given that it's hard to find users who are asking for copy restriction features, one might think that this would be an ideal place for the Debian developers in charge of Okular to provide a more friendly default. But they do not want to do that. Okular developer Pino Toscano justifies the copy-restriction antifeature by saying that it's part of the PDF format specification. Since Okular is meant to follow the standard, it must do so in this case as well. Beyond that, Pino says:

Additionally, Debian KDE maintainer Sune Vuorela claims that the overhead of maintaining a patch to Okular would exceed the value gained - though it has been pointed out that the patch is trivial - and that the real problem is that people are downloading PDF files with restrictions in the first place. He states that Okular should not help users to "violate the conditions of use" associated with the file, but does not say why, if that is a concern, the ability to ignore copy restrictions is not patched out altogether.

Beyond that, others have raised concerns that failure to enforce copy restrictions could lead to legal problems in some jurisdictions. It is not clear which jurisdictions those would be, though. The copying of excerpts is allowed by fair use rules almost everywhere. Even the DMCA should not come into play here; the "do not copy" flag is simply a piece of advice found in the file which does not constitute an "effective technological measure" in any way. There has been a distinct shortage of legal problems (or even threats) associated with any of the other PDF readers which fail to implement this particular behavior. And, if such threats did exist, the existence of an option to ignore copy restrictions would be problematic regardless of its default value.

The evince PDF reader ran into this issue back in 2005. It is now rare to find a distributor shipping a version of evince which implements copy restrictions. Xpdf implements copy restrictions unconditionally, but Debian patched that code out in 2002, and that patch has spread to other distributors as well. In general, as one would expect, free PDF readers tend not to implement this behavior. Okular is about the only exception that your editor can find; it's interesting to note that the version of Okular shipped with Fedora Rawhide also implements copy restrictions by default. Perhaps this behavior is result of the relative newness of this application; as it accumulates more users, the pressure for more user-friendly behavior is likely to grow.

As that pressure mounts, Okular's developers and packagers may find it hard to justify keeping copy restrictions in place. Linux, at all levels, has felt free to ignore standards when following them makes no sense. And one could argue that the copy-restriction flag - which interferes with fair-use rights while doing nothing to prevent copying of the file or its contents - makes little sense indeed. This is not a feature which adds value for Linux users; such features still tend to disappear over time.

Original link: http://lwn.net/Articles/335415/