I added support for the '\ ' PostScript escaped space sequence to a custom, high-performance PDF parser.
A former employer used this to derive key figures from financial statements. Any change to the parser had to be Pareto-optimal: so if you modified the parser, it should not fail to parse any key figure that was previously possible to parse. Adding this improved reading word-wrapped text in hundreds of cases and key figures in dozens; I recall that my bosses thought it must be a mistake, and that I had to convince them by finding the right section in some Adobe PDF spec.
I wasn't an expert at the PDF format. But stumbling on a number split in two by apparently nothing, and digging up a 0x5C 0x20 '\ ' with a hex editor, I seemed to recall that PDF was built on top of PostScript, and that TeX / LaTeX syntax was somehow related to PostScript. So it struck me that what was a literal backslash in the PDF must just be an escape sequence.
