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Getting a full PDF from a DRM-encumbered online textbook
- pdw 11y agoWatermarks and such are easy to remove with PDFtk, the swiss army knife of PDF files. Convert the input files to a plain-text representation, find the code that implements the watermark (it will be the only code that's identical on every page), delete it and convert back. Easy as pie. It will also concatenate the partial files.
- semi-extrinsic 11y agoHow does that preserve things like layout or equations? I've done similar (though usually less effort) textbook trickery a few times. The Adobe Inept hack is very handy. Oh, and a recent one was stupidly easy: you could view the ebook in your browser, and save excerpts as a pdf, but only 100 pages in total per book. Problem was it stored how many pages you had saved in a cookie, so "Clear the last 5 minutes of browsing history" and you could get another 100 pages, rinse and repeat for all the book and then staple the files together with pdftk.
- function_seven 11y agoI think the "plain text representation" parent is referring to is the PostScript that defines the page. If the equations are rendered in PS, or are inline images, they might survive the roundtrip conversion?
- pdw 11y agoYes, it's a jumble of PostScript fragments, base64-encoded images and PDF metadata. Everything that's needed to reconstruct the original PDF, but in a form that's safe to edit in a text editor.
- scintill76 11y agoYou might want to compress the PDF again when you're done (my understanding is that part of what makes PDFs non-plain-text is binary compression encodings within the PDF container.)
- SomeCallMeTim 11y agoYeah, that was what I was thinking. PDFs typically are full of Postscript (except if they're just scanned images), which is just a text rendering language. As long as you keep the Postscript format valid, you could remove the watermark by just deleting that text. I didn't know about PDFtk, but Ghostscript can take a PDF and turn it into text Postscript, and it can reverse the process.
- aidenn0 11y agoghostscript has always either rasterized or converted to individual strokes embedded fonts when I try that, but there's like 50 options for pdf->ps so perhaps I've got it wrong.
- sosuke 11y agoPDFtk won't work with some of the more modern PDFs. Adobe added in another layer, kept the same extension and blocked out most of the 3rd party readers. Some tool called LiveCycle I think. But for normal PDFs PDFtk is incredibly useful!
- jimjimjim 11y agolivecycle is only really used for interactive forms and it's not part of the pdf spec.
- userbinator 11y agoI agree; it's a fun and inspiring story, and the automation is great, but IMHO getting a PDF of a DRM'd book which consists entirely of bitmap images of each page is near the bottom of my list of options if I were in the same situation; it's probably somewhat above the "analogue hole" option of taking a picture of each page with a camera pointed at the monitor. Unless that's what the downloaded PDF consisted of, it would be far better to work with the PDF directly since it is intrinsically a vector format and removing the watermarks from the page content stream that way (it's a PostScript-like language) would be superior in terms of filesize and quality. A few years ago I was involved in a project that required capturing content from an online document viewer site that used a SWF for each page, and our product basically did a vector-vector conversion from SWF to PDF. One of our competitor's product did the "render each page as an image, and combine the images into a PDF" and the output difference was amazing. IIRC it was around 2 orders of magnitude in size, and 4 in speed of generation. (They used Java, and we used C, which might account for some of that too, so it's not a totally fair comparison.)
- DanBC 11y agoI'm glad he did it, and published the result. But isn't cracking DRM a criminal offence? Is it wise to confess to it in a public forum?
- shmerl 11y agoCracking DRM should not be an offense if you already bought that thing. Except that DRM lobby declared it illegal (it's a corrupted anti-circumvention law).
- wolfgke 11y ago"There is no justice in following unjust laws." - Aaron Swartz Source: https://archive.org/stream/GuerillaOpenAccessManifesto/Goamjuly2008_djvu.txt https://archive.org/stream/GuerillaOpenAccessManifesto/Goamj... (https://archive.org/details/GuerillaOpenAccessManifesto https://archive.org/details/GuerillaOpenAccessManifesto)
- shmerl 11y agoIndeed, that's why DRM was broken and will be broken despite any attempts of DRM lobby to proliferate it.
- chris_wot 11y agoThey would have to prove the book he actually cracked.
- gohrt 11y agoDRM-laden online books is a red flag that the college you are attending is a thinly veiled profit center, not an education provider. Has anyone made an index of which colleges require DRM textbook purchases in their courses?
- lfowles 11y agoGoing to guess 95%+ make use of online access codes in freshman classes. Saves the TAs for upper level classes.
- spectralblu 11y agoI had encountered this in the lower div general education courses at my university. The most egregious one was the professor who required us to get the current edition of the textbook (since he would be assigning problems out of the new book, which was just a shuffled version of the previous version) that he wrote himself. Fitting that it was an economics course. Once I got into the CS courses, most if not all of my professors just provided PDFs of either their own material or some open source textbook they were contributing to.
- sotojuan 11y ago> DRM-laden online books is a red flag that the college you are attending is a thinly veiled profit center, not an education provider. So then most US colleges? Like spectralblu said, this is common in lower level classes—especially math classes for some reason.
- sotojuan 11y agoAs someone interested in Clojure, it's cool to see stuff like this build with it. Luckily I haven't needed to purchase expensive books since freshman year. Everything I've been required to I either rent on Amazon for $30 or find online.
- aftbit 11y agoI've done the same thing before on a book in college, except my DRM wasn't nice enough to let me print 10 pages at a go. Instead, I spun up a virtual X server with Xdummy with a resolution of 1200x10000. That showed a few dozen pages at a time. Then I automated screenshots (scrot) and PageDown (xdotool). Finally, some PIL magic to look for the thin gray line between pages plus convert and ghostscript and I had a PDF!
- deleted 11y ago[deleted]
- mixedmath 11y agoI notice he said the final product was around 700 megabytes, which is a bit absurd. What could he have done to make the final size more reasonable?
- a_bonobo 11y agoThe PNGs are insanely high resolution I think so that the OCR works better - it doesn't say, but I assume the OCR'd book can use lower resolution.
- mixedmath 11y agoI notice he said the final product was around 700 megabytes, which is a bit absurd. What could he have done to make the final size more reasonable?
- Johnny_Brahms 11y agoI have this idea that any material that uses DRM should not be covered by copyright simply because it removes itself from things that will end up in the public domain. For me, one of the wonderful things about copyright is that works always end up available for free to the general public. A DRMed work will never be free in that sense, and should then not be covered by the regular legal protections.
- lispit 11y agoAs long as Disney is around, nothing will ever enter the public domain again.
- Johnny_Brahms 11y agoTTIP and similar deals fucks it up for the rest of us as well. I say a maximum of 25 years free copyright (i'd rather see something like 5-10 years), and then progressively increasing fees that start becoming crazy after something like ten years. Then use that money to finance culture.