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History of the PDF

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Re: History of the PDF

#31

Post by JKCalhoun »

ralferoo wrote: post #29
JKCalhoun wrote: post #22

Earlier quoted context omitted.

Most often the text runs you would extract from a PDF are in the order you would read the text. Probably because the word processor or application that created the PDF dumped the text into the capturing PDF context from its own text container that, in fact, contains the text in the order the word processor would display it (editing, searching, text selection in the creating app obviously benefit if the text container…

It's true that data is often written out in a logical order, but like you say, that's only because the program that created it was designed that way. I've definitely seen PDF files where tabular data is almost in a logical order but every now and then cells have been jumbled around. But what I've definitely seen is documents where the characters are deliberately jumbled up and a custom font so that visually everythin…

To be sure, the content-creator can run riot with the PDF spec and make it suck for everyone but a human reading the screen or printed page. Fortunately I would say 99% of PDFs are much better behaved than that.

Re: History of the PDF

#32

Post by divbzero »

From page 12 of the PDF:

> Comments on places like HackerNews refer to it as “one of the worst file formats ever produced” [1], “soul-crushing” [2], and something that “should really be destroyed with fire” [3].

I found the source for [1] and [3] https://news.ycombinator.com/item?id=22474460 but couldn’t identify the source of [2].

Re: History of the PDF

#33

Post by ogurechny »

martin_a wrote: post #28

For everybody complaining about the non-transformative character of PDF: There are several PDF standards out in the wild. In the graphic industry we mainly use PDF/X files. These are very solid and precise in defining the layout and how objects are rendered. For archiving purposes there's another standard, it's called PDF/A. Part of PDF/A is that you must be able to transform its text content back to Unicode. So, if…

PDF/A is a joke of a “standard” that does almost nothing that is promised on the cover. It is just a subset of PDF with limits on variable options like color representation, frozen at some arbitrary point in time, probably because people working with digital archives realized that they couldn't reach the moving goal, and implement the ever growing list of features. We may only expect programs producing PDF/A files to be less “creative”, and produce straightforward markup, but it's not guaranteed at all, because PDF/A doesn't address any of the real core format issues.

Re: History of the PDF

#34

Post by herodotus »

After working on PDF document reconstruction for more than a decade, I often fantasized about inventing a cleaner and simpler alternative. After all, there are only three kinds of objects in PDF: shapes, images and glyphs. But it is all those little details that will get you in the end. A line - all you need is a coordinate and a length, right? No: is it solid, what is its width? Is its end point anchored on the left most part of the visible line, or does the thickness spread out from the anchor point? And is the end square of curved? If curved, what are the parameters of the curve? Are both ends the same? On it on it goes. And don't event get me started on glyphs...

PDF is a remarkable creation. It has some notable weaknesses, such as the fact that its color channel for images does not include alpha, and thus needs masks, but the fact that it covers so much visual complexity in a relatively compact form is just amazing. (BTW: Its graphics model is strictly from Adobe Postscript, but PDF content streams are not programs.)

One thing that bugged me while reading this article was the use of the definite article ("the PDF"). Since PDF is an acronym for "Portable Document Format" there may be a grammatical case to be made for the "the", but no one says "the HTML" or "the NASA" and so on.

Re: History of the PDF

#35

Post by Tangurena2 »

ralferoo wrote: post #12

So, reading the article is a bit weird. It's clear there's an anti-PDF bias from the start, with the implicit assumption that everybody hates reading PDF files. Actually, I don't because I get to read a well formatted document. They even say that it should only be used as a format for things to be printed, never as a document for people to read on a computer... and yet this is clearly meant to be read once on a scree…

Mostly, the page description language (inside PDFs) says "move to point (x, y) and write text foo" or "move to point (x, y) and draw glyph bar".

The reason that many PDFs produce garbage when extracting text is because the underlying document doesn't include fonts, every letter is a drawn glyph. This is most common in older (1990s) pdfs generated on UNIX systems.

Since the page description language is saying "write text foo", that text is broken up by the generating software, so there is not necessarily a whole line of text as a human would see it.

And some PDFs are impossible to extract text from because they've flattened the page into an image. Law firms are notorious for doing this - to provide the documents exactly as required/specified during discovery, but make them impossible for the text to be extracted. Basically it is a fax - every page is a TIFF image (because it is harder to OCR than a JPEG, although JBIG2 has its own flaws [0]).

I've been working with PDF projects off and on since the late 90s. The standard tries to be everything for everybody and that makes it a Charlie Foxtrot from top to bottom (if you've ever written an object viewer/editor to dig inside PDFs, you know exactly what I'm referring to). It is a great spec for making a document that appears the same no matter where it is viewed or printed. But I always treat it as a sausage: you can turn the cow into a sausage, but you can't turn that sausage back into a cow.

0 - https://www.theverge.com/2013/8/6/4594482/xerox-copiers-rand...

Re: History of the PDF

#36

Post by signaru »

contrarian1234 wrote: post #17

Are there any real alternatives? I tried to make a conference poster with SVG - using Inkscape - and it was minor disaster that rendered differently in different programs/browsers, with some features entirely broken but I don't know of a third option..

Microsoft tried with XPS which is a zipped XML format, pretty much like MS Office 2007+ files. To Adobe's credit, they made PDF an open standard around the time XPS came out. Maybe it's a combination of being there first, many files already in PDF, and finally making the format open which made PDF win.

Re: History of the PDF

#37

Post by epc »

contrarian1234 wrote: post #17

Are there any real alternatives? I tried to make a conference poster with SVG - using Inkscape - and it was minor disaster that rendered differently in different programs/browsers, with some features entirely broken but I don't know of a third option..

IBM tried to push a competitor in the 1990s…BookManager was an initially mainframe (VM/CMS, MVS, etc) combination of viewer program and proprietary format. It came about in response to both IBM customers and product documentation groups demanding some sort of online “hypertext” version of the thousands of publications available.

IIRC it came out around the same time as the initial Acrobat format but not necessarily in response to it. Eventually there were viewers for Windows, OS/2. It wasn't particularly bad, but it was very literal in display and Acrobat/PDF rapidly left it in the dust.

When the web boomed in 1995–1996 the product group behind BookManager tried to ban distribution of PDFs by other IBM groups but failed. One of the problems with BookManager formatted files is you had to recreate the appropriate record format if you transferred it back to a mainframe, and I vaguely recall EBCDIC vs ASCII issues (where PDF is, I think, UTF native?).

https://en.wikipedia.org/wiki/SCRIPT_(markup)#BookManager

Re: History of the PDF

#38

Post by FuriouslyAdrift »

contrarian1234 wrote: post #17

Are there any real alternatives? I tried to make a conference poster with SVG - using Inkscape - and it was minor disaster that rendered differently in different programs/browsers, with some features entirely broken but I don't know of a third option..

There's DVI (device independent file format) from TeX

https://en.wikipedia.org/wiki/Device_independent_file_format

Re: History of the PDF

#40

Post by Someone »

ralferoo wrote: post #12

So, reading the article is a bit weird. It's clear there's an anti-PDF bias from the start, with the implicit assumption that everybody hates reading PDF files. Actually, I don't because I get to read a well formatted document. They even say that it should only be used as a format for things to be printed, never as a document for people to read on a computer... and yet this is clearly meant to be read once on a scree…

> fonts that are designed to obfuscate the internal text, e.g. re-arranging characters or splitting glyphs up in strange ways, etc. It's worth noting that with the exception of the spaces, these techniques are used deliberately to stop people extracting text or the copyrighted fonts from the document.

Maybe (and, for the fonts, likely), but I don’t think it’s the only reason. Subsetting embedded fonts makes PDFs smaller, often a lot smaller (why embed an entire font because the document uses a single glyph of it as a bullet point? Why would one include Chinese, Japanese, etc glyphs if the document doesn’t use them?)

Even if it’s possible to do that without changing the code point to glyph mapping (is it? I don’t know enough of fonts to answer that), implementing it may be simpler or result in smaller files if one makes the embedded font dense in code points (I tried finding an answer, but soon remembered how complex fonts are, and gave up)

And of course, modern tools _should_ output accessible PDF documents, which means text extraction _should_ work. I wouldn’t know how well that works in reality, but have my doubts.

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