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I have some research papers in PDF format that are actually scanned (and then OCRed) instead of being the original PDF. Some are so badly created that text cannot be properly searched inside.

For example this paper published in 1994 is all about advanced computer technology and there is no proper digital copy. This extended report related to the above paper is even more horribly digitized.

edit: I am unable to access the actual horribly scanned paper. That extended report also had issues in copying.

Why is that? Why are some computer-science publications, which are not even so old, not available in a proper digital format?

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    I fail to see any hints that the second document has been scanned or OCRed. The only thing I see that impedes searchability is due to standard LaTeX’s encoding of ligatures, which is unfortunately somewhat backwards. – Wrzlprmft Apr 26 '15 at 17:21
  • Yeah, it looks like the second document has been converted from a postscript file that used bitmapped fonts (which would explain why it looks bad but shows no signs of being scanned). – Anonymous Mathematician Apr 26 '15 at 18:41
  • @Wrzlprmft I am unable to access the actual [horribly scanned paper] (dl.acm.org/citation.cfm?id=239773&preflayout=tabs). That extended report also had issues in copying. – LifeH2O Apr 26 '15 at 18:58
  • The second link appears to be converted to PDF from an old PS file. Perfectly digital, just technologically outdated. pdflatex hasn't always been around, and people had to go through PS to create PDF files. – darij grinberg Apr 26 '15 at 19:18
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In many cases, even through the early 2000's, publishers produced print journals using older type setting systems and did not produce PDFs of the papers for online publication. Once the papers were type set for printing, the publisher might have discarded all of the files associated with the papers or they might have just kept a file containing a print-ready image of the paper.

Many journals had old material of this sort dating back decades. Since it would take a huge effort to type-set all of those older papers again, journal publishers have settled for simply scanning the earlier papers (or retrieving saved images of the papers) and then publishing the images of the papers online.

Using optical character recognition (OCR) is one way to extract the text from these images. However, OCR isn't 100% accurate, and in any case it can't preserve all of the formatting of the paper. Thus OCR text from a scanned image of a published paper may be somewhat useful for indexing, but it really isn't equivalent to having the original document as a text PDF.

A different issue is that you may have received a copy of a paper from someone other than the publisher. For example, if you made an inter library loan request to get a copy of a paper, it's possible that someone at another university library scanned a printed copy of the paper and sent that scan to you.

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PDF is a younger format than you think it is, having only been invented in 1993. Before that, documents would have been in PostScript at best. Many things you might think are OCR are actually bad PS conversions: it is very hard to unscramble the PS egg in some cases. The first linked paper appears to be of that type.

For others where is no version even that good, it is simply that the cost of a better conversion is higher than the value per old paper. Maybe this will change someday, but right now the high quality OCR systems have higher priorities.

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