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From: Rich <rich@example.invalid>
Newsgroups: misc.news.internet.discuss,comp.misc
Subject: Re: China: Government Starts Phasing Out American Processors, Operating Systems on Government Computers
Date: Sun, 31 Mar 2024 02:10:09 -0000 (UTC)
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In comp.misc Mike Spencer <mds@bogus.nodomain.nowhere> wrote:
> 
> kludge@panix.com (Scott Dorsey) writes:
> 
>> You also would see a lot of weird ligatures back then which are seldom
>> seen today.   Some of that stuff didn't actually disappear until automated
>> typesetting came along, as there are only so many keys on the linotype.
> 
> ...
> 
> The PDF author had used used the ff ligature from whatever
> $CURRENTLY-KEWL-CHARSET which was rendered readably.  But the xpdf
> author wasn't clueful enough to realize that no user ever enters a
> ligature character code from the keyboard as a search target and write
> compensating translations into the source code.

It may not be xpdf's author's fault.  If the pdf creator did not 
provide a proper reverse map table from the code point used for the ff 
ligature to its actual character (or characters) then there's nothing a 
pdf reader can do to fix the problem.

The problem is that the PDF specification allows for the PDF creator to 
create arbitrary mappings from byte values used in the PDF file to any 
given glyph in a font file.  But it makes optional the reverse mapping 
table which would define to a PDF reader program that "byte value 0x32 
in this portion of this PDF [1] represents the 'ff' litgature".  
Without that reverse table, PDF is effectively a "write only medium".  
It will print a perfect document, but you can't search, nor copy out, 
anything from it.


[1] 0x32 can be made to represent any number of different glyphs within 
a single given PDF.  In fact, if one were so devious as to do so, every 
byte in the pdf representing a text character could be 0x32, and each 
one could "print" to the electronic sheet of paper a different font 
glyph.