pdf

21 Articles

Screenshot of Linux in a PDF in a browser

Nice PDF, But Can It Run Linux? Yikes!

February 10, 2025 by 21 Comments

The days that PDFs were the granny-proof Swiss Army knives of document sharing are definitely over, according to [vk6]. He has managed to pull off the ultimate mind-bender: running Linux inside a PDF file. Yep, you read that right. A full Linux distro chugging along in a virtual machine all encapsulated within a document. Just when you thought running DOOM was the epitome of it. You can even try it out in your own browser, right here. Mind-boggling, or downright Pandora’s box?

Let’s unpack how this black magic works. The humble PDF file format supports JavaScript – with a limited standard library, mind you. By leveraging this, [vk6] managed to compile a RISC-V emulator (TinyEMU) into JavaScript using an old version of Emscripten targeting asm.js instead of WebAssembly. The emulator, embedded within the PDF, interfaces with virtual input through a keyboard and text box.

The graphical output is ingeniously rendered as ASCII characters – each line displayed in a separate text field. It’s a wild solution but works astonishingly well for something so unconventional.

Security-wise, this definitely raises eyebrows. PDFs have long been vectors for malware, but this pushes things further: PDFs with computational power. We know not to trust Word documents, whether they just capable of running Doom, or trash your entire system in a blink. This PDF anomaly unfolds a complete, powerful operating system in front of your very eyes. Should we think lightly, and hope it’ll lead to smarter, more interactive PDFs – or will it bring us innocent looking files weaponized for chaos?

Curious minds, go take a look for yourself. The project’s code is available on GitHub.

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You Can Now Play DOOM In Microsoft Word, But You Probably Shouldn’t

January 20, 2025 by 23 Comments

DOOM used to primarily run on x86 PCs. It later got ported to a bunch of consoles with middling success, and then everything under the sun, from random embedded systems to PDFs. Now, thanks to [Wojciech Graj], you can even play it in Microsoft Word.

To run DOOM inside Microsoft Word, you must enable VBA macros, and ignore security warnings, to boot. You’ll need a modern version of Word, and it will only work on Windows on an x64 CPU. As you might imagine, too, the *.DOCM file is not exactly lightweight. It comes in at 6.6 MB, no surprise given it contains an entire FPS. It carries inside it a library called doomgeneric_docm.dll and the whole doom1.wad data file. Once the file is opened, a macro then extracts all the game data and executes it.

If you think that Microsoft Word doesn’t really have a way of displaying live game graphics, you’d be correct. Instead, that DLL is creating a bitmap image of the game state for every frame, which is then displayed inside Word itself. It uses the GetAsyncKeyState function to grab inputs from the arrow keys, number keys, and CTRL and space so the player can move around. It certainly sounds convoluted, but it actually runs pretty smoothly given all the fuss.

While this obviously works, you shouldn’t get in the habit of executing random code in your word processor. It’s just not proper, you see, like elbows on the dinner table! And, you know. It’s insecure. So don’t do that.

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Nice PDF, But Can It Run DOOM? Yup!

January 15, 2025 by 12 Comments

DOOM is a classic game to implement on a variety of platforms, but doompdf by [ading2210] is one we didn’t see coming. It runs a bit slow and controls are a little awkward but it does run. Entirely within a PDF file, at that.

How is this possible? PDFs are technically capable of much more than just displaying static content, and support JavaScript with their own library of functions. Adobe Acrobat implements the full spec, but modern web browsers implement at least a subset of the functionality in a sandboxed JavaScript runtime environment. Input and output are limited to things one might expect from a fancy PDF form (text input boxes, clickable buttons, things of that nature) but computation-wise, just about anything goes.

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Keeping Track Of Old Computer Manuals With The Manx Catalog

December 24, 2024 by 4 Comments

An unfortunate reality of pre-1990s computer systems is that any manuals and documentation that came with them likely only existed on paper. That’s not to say there aren’t scanned-in (PDF) copies of those documents floating around, but with few of these scans being indexable by search engines like Google and Duck Duck Go, they can be rather tricky to find. That’s where the Manx catalog website seeks to make life easier. According to its stats, it knows about 22,060 manuals (9,992 online) across 61 websites, with a focus on minicomputers and mainframes.

The code behind Manx is GPL 2.0 licensed and available on GitHub, which is where any issues can be filed too. While not a new project by any stretch of the imagination, it’s yet another useful tool to find a non-OCR-ed scan of the programming or user manual for an obscure system. As noted in a recent Hacker News thread, the ‘online’ part of the above listed statistics means that for manuals where no online copy is known, you get a placeholder message. Using the Bitsavers website along with Archive.org may still be the most pertinent way to hunt down that elusive manual, with the Manx website recommending 1000bit for microcomputer manuals.

Have you used the Manx catalog, or any of the other archiving websites? What have been your experiences with them? Let us know in the comments.

Back Up Your Data On Paper With Lots Of QR Codes

September 12, 2024 by 55 Comments

QR codes are used just about everywhere now, for checking into venues, ordering food, or just plain old advertising. But what about data storage? It’s hardly efficient, but if you want to store your files in a ridiculous paper format—there’s a way to do that, too!

QR-Backup was developed by [za3k], and is currently available as a command-line Linux tool only. It takes a file or files, and turns them into a “paper backup”—a black-and white PDF file full of QR codes that’s ready to print. That’s legitimately the whole deal—you run the code, generate the PDF, then print the file. That piece of paper is now your backup. Naturally, qr-backup works in reverse, too. You can use a scanner or webcam to recover your files from the printed page.

Currently, it achieves a storage density of 3KB/page, and [za3k] says backups of text in the single-digit megabyte range are “practical.” You can alternatively print smaller, denser codes for up to 130 KB/page.

Is it something you’ll ever likely need? No. Is it super neat and kind of funny? Yes, very much so.

We’ve seen some other neat uses for QR codes before, too—like this printer that turns digital menus into paper ones. If you’ve got your own nifty uses for these attractive squares, let us know!

Get That Dream Job, With A Bit Of Text Injection

May 20, 2023 by 28 Comments

Getting a job has always been a tedious and annoying process, as for all the care that has been put into a CV or resume, it can be still headed for the round file at the whim of some corporate apparatchik. At various times there have also been dubious psychometric tests and other horrors to contend with, and now we have the specter of AI before us. We can be tossed aside simply because some AI model has rejected our CV, no human involved. If this has made you angry, perhaps it’s time to look at [Kai Greshake]’s work. He’s fighting back, by injecting a PDF CV with extra text to fool the AI into seeing the perfect candidate, and even fooling AI-based summarizers.

Text injection into a PDF is a technique the same as used by the less salubrious end of the search engine marketing world, of placing text in a web page such that a human can’t read it but a machine can. The search engine marketeers put them in tiny white text or offset them far out of the viewport, and it seems the same is possible in a PDF. He’s put the injection in white and a tiny font, and interestingly, overlaid it several times.

Using the ChatGPT instance available in the Bing sidebar he’s then able to fool it into an affirmative replay to questions about whether he should be hired. But it’s not just ChatGPT he’s targeting, another use of AI in recruitment is via summarizing tools. By injecting a lot of text with phrases normally used in conclusion of a document, he’s able to make Quillbot talk about puppies. Fancy a go yourself? He’s put a summarizer online, in the link above.

So maybe the all-seeing AI isn’t as clever as we’ve been led to believe. Who’d have thought it!

Compare PDFs Visually

August 6, 2022 by 12 Comments

Sometimes a problem seems hard, but the right insight can make it easy. If you were asked to write a program to compare two PDF files and show the differences, how hard do you think that would be? If you are [serhack], you’ll make it much easier than you might guess.

Of course, sometimes making something simple depends on making simplifying assumptions. If you are expecting a “diff-like” utility that shows insertion and deletions, that’s not what’s going on here. Instead, you’ll see an image of the PDF with changes highlighted with a red box. This is easy because the program uses available utilities to render the PDFs as images and then simply compares pixels in the resulting images, drawing red boxes over the parts that don’t match.

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