喂食
\documentclass{article}
\usepackage{graphicx}
\begin{document}
\includegraphics{included_file.pdf}
\end{document}
对于 xelatex，我们得到了预期的 PDF 输出，但是
invalid 13 0 R object at offset 259693
invalid 13 0 R object at offset 259693
在控制台上（不在日志中）：
$ xelatex mwe
This is XeTeX, Version 3.141592653-2.6-0.999993 (TeX Live 2022/dev/Debian) (preloaded format=xelatex)
restricted \write18 enabled.
entering extended mode
(./mwe.tex
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2021-11-22>
(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2021/10/04 v1.4n Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo))
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-def/xetex.def)))
(/usr/share/texlive/texmf-dist/tex/latex/l3backend/l3backend-xetex.def
(|extractbb --version)) (./mwe.aux)
(/usr/share/texlive/texmf-dist/tex/latex/base/ts1cmr.fd)
invalid 13 0 R object at offset 259693
invalid 13 0 R object at offset 259693
[1] (./mwe.aux) )
Output written on mwe.pdf (1 page).
Transcript written on mwe.log.
以下是所附 pdf 中的一些数据：
$ pdfinfo included_file.pdf
Title: D:uploadedFile0cc7c497eb35f2a11447e94640dc1f-1bd5194ff4bb7acp1a120c7k41f6fedp15rf1gg11j0m.pdf
Producer: ImageMagick 6.6.1-7 2010-05-07 Q8 http://www.imagemagick.org
CreationDate: Wed Oct 7 17:37:59 2015 CEST
ModDate: Wed Oct 7 17:37:59 2015 CEST
Tagged: no
UserProperties: no
Suspects: no
Form: none
JavaScript: no
Pages: 1
Encrypted: no
Page size: 59.52 x 55.92 pts
Page rot: 0
File size: 260480 bytes
Optimized: no
PDF version: 1.3
由于签署了保密协议，很遗憾，我无法向读者提供随附的 PDF 本身。（它是由我的同事内部生成的，无法在线获取，并且无法再轻松重新生成。）
运行 lualatex 而不是 xelatex 会发出相同的警告消息：
$ lualatex mwe
This is LuaHBTeX, Version 1.14.0 (TeX Live 2022/dev/Debian)
restricted system commands enabled.
(./mwe.tex
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2021-11-22>
(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2021/10/04 v1.4n Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo))
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-def/luatex.def)))
(/usr/share/texlive/texmf-dist/tex/latex/l3backend/l3backend-luatex.def)
(./mwe.aux) (/usr/share/texlive/texmf-dist/tex/latex/base/ts1cmr.fd)
(/usr/share/texlive/texmf-dist/tex/context/base/mkii/supp-pdf.mkii
[Loading MPS to PDF converter (version 2006.09.02).]
) (/usr/share/texlive/texmf-dist/tex/latex/epstopdf-pkg/epstopdf-base.sty
(/usr/share/texlive/texmf-dist/tex/latex/latexconfig/epstopdf-sys.cfg))
warning (file included_file.pdf) (pdfe): invalid 13 0 R object at offset 25969
3
[1{/var/lib/texmf/fonts/map/pdftex/updmap/pdftex.map}<./included_file.pdf
warning (pdfe): invalid 13 0 R object at offset 259693
>] (./mwe.aux))
(see the transcript file for additional information)
406 words of node memory still in use:
3 hlist, 1 vlist, 1 rule, 2 glue, 3 kern, 1 glyph, 4 attribute, 48 glue_spec
, 4 attribute_list, 1 write nodes
avail lists: 1:1,2:35,3:4,4:1,5:23,6:2,7:34,9:38
</usr/share/texmf/fonts/opentype/public/lm/lmroman10-regular.otf>
Output written on mwe.pdf (1 page, 221730 bytes).
Transcript written on mwe.log.
运行 pdflatex 而不是 UTF-8 引擎不会出现任何警告。无论使用哪种引擎，生成的 PDF 文件在视觉上似乎都相同。
这个警告到底告诉我们什么？我们应该担心还是尝试修复 PDF（解压并破解）？