This seemingly valid PDF gets curiously broken, when converted by pdftocairo into level 3 PS or PDF, letters i and l are missing from the result.
Cairo 1.14.12, poppler-utils 0.53.0, both commands produce a resulting PDF or PS where letters i and l are missing:
pdftocairo -ps -level3 isandlsmissing.pdf is-cairo53.ps
pdftocairo -pdf isandlsmissing.pdf is-cairo53.pdf
Same commands produce correct files on Ubuntu 14.04, cairo 1.13.1, poppler-utils 0.24.5.
pdftocairo -ps -level3 isandlsmissing.pdf is-cairo24.ps
pdftocairo -pdf isandlsmissing.pdf is-cairo24.pdf
Original PDF was validated with Adobe Pro DC, no syntax errors found. Here is the report.
Preflight Summary Report for: isandlsmissing.pdf
Profile: Report PDF syntax issues (Processed pages 1 to 1)
Results (Summary): No problems found
File name: "isandlsmissing.pdf"
PDF version number: "1.7"
File size (KB): 59.2
Created: "2/13/2018 2:48 PM"
Preflight, 15.2.0 (199)
Acrobat version: 18.90
Also attached are PDF and PS results produced by pdftocairo version 0.24.5 (is-cairo24.ps, pdf) and version 0.53.0 (is-cairo53.pdf,ps)
Created attachment 137328 [details]
Created attachment 137329 [details]
Created attachment 137330 [details]
Created attachment 137331 [details]
Created attachment 137332 [details]
Reproduced on Debian testing (buster), poppler 0.61.1, cairo 1.14.10.