使用Ghostscript合并PDF时字体损坏问题的排查与修复咨询

尝试用Ghostscript合并PDF文件时遇到字体问题：标准拉丁文字符显示正常，但非标准字符（疑似CID字体）显示异常，尽管原文件和输出文件标称使用同一字体。

执行的命令及输出（已整理换行和编号）：

$ gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=out.pdf in.pdf
GPL Ghostscript 9.26 (2018-11-20)
Copyright (C) 2018 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
Processing pages 1 through 1.
Page 1
-- 1
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPSMT.
Can't find (or can't open) font file TimesNewRomanPSMT.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPSMT.
Can't find (or can't open) font file TimesNewRomanPSMT.
Querying operating system for font files...
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPSMT.
Can't find (or can't open) font file TimesNewRomanPSMT.
Didn't find this font on the system!
Substituting font Times-Roman for TimesNewRomanPSMT.
Loading NimbusRoman-Regular font from /usr/share/ghostscript/9.26/Resource/Font/NimbusRoman-Regular... 5046332 3572454 3115872 1726420 4 done.

-- 2
Can't find CID font "TimesNewRoman".
Attempting to substitute CID font /Adobe-Identity for /TimesNewRoman, see doc/Use.htm#CIDFontSubstitution.
The substitute CID font "Adobe-Identity" is not provided either. attempting to use fallback CIDFont.See doc/Use.htm#CIDFontSubstitution.
Loading a TT font from /usr/share/ghostscript/9.26/Resource/CIDFSubst/DroidSansFallback.ttf to emulate a CID font Adobe-Identity ... Done.

-- 3
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPS-ItalicMT.
Can't find (or can't open) font file TimesNewRomanPS-ItalicMT.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPS-ItalicMT.
Can't find (or can't open) font file TimesNewRomanPS-ItalicMT.
Didn't find this font on the system!
Substituting font Times-Italic for TimesNewRomanPS-ItalicMT.
Loading NimbusRoman-Italic font from /usr/share/ghostscript/9.26/Resource/Font/NimbusRoman-Italic... 9238300 7844767 3270416 1870892 4 done.

-- 4
Can't find CID font "TimesNewRoman".
Attempting to substitute CID font /Adobe-Identity for /TimesNewRoman, see doc/Use.htm#CIDFontSubstitution.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPS-BoldMT.
Can't find (or can't open) font file TimesNewRomanPS-BoldMT.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/TimesNewRomanPS-BoldMT.
Can't find (or can't open) font file TimesNewRomanPS-BoldMT.
Didn't find this font on the system!
Substituting font Times-Bold for TimesNewRomanPS-BoldMT.
Loading NimbusRoman-Bold font from /usr/share/ghostscript/9.26/Resource/Font/NimbusRoman-Bold... 9486596 8090953 3465360 2062449 4 done.

-- 5
Can't find CID font "TimesNewRoman".
Attempting to substitute CID font /Adobe-Identity for /TimesNewRoman, see doc/Use.htm#CIDFontSubstitution.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/Arial-BoldMT.
Can't find (or can't open) font file Arial-BoldMT.
Can't find (or can't open) font file /usr/share/ghostscript/9.26/Resource/Font/Arial-BoldMT.
Can't find (or can't open) font file Arial-BoldMT.
Didn't find this font on the system!
Substituting font Helvetica-Bold for Arial-BoldMT.
Loading NimbusSans-Bold font from /usr/share/ghostscript/9.26/Resource/Font/NimbusSans-Bold... 9735428 8335065 3720904 2297241 4 done.

-- 6
Can't find CID font "Arial".
Attempting to substitute CID font /Adobe-Identity for /Arial, see doc/Use.htm#CIDFontSubstitution.
Can't find CID font "Arial".
Attempting to substitute CID font /Adobe-Identity for /Arial, see doc/Use.htm#CIDFontSubstitution.

咨询问题 #

1. CID font究竟是什么？
2. 如何解决字体显示异常问题？
3. 如何通过Ghostscript将原PDF中的嵌入字体复制到新生成的PDF中？

1. 什么是CID字体？ #

CID（Character Identifier）字体是专为大字符集设计的字体格式，常用于中文、日文、韩文这类包含大量字符的语言场景。和传统PostScript字体最多支持256个字符的限制不同，CID字体通过唯一的字符ID映射字符，能容纳上万甚至更多字符，专门解决多文种、复杂字符的排版需求。日志里提到的TimesNewRoman、Arial CID字体，是对应西文字体的大字符集版本，支持非标准拉丁字符或其他语言字符。

2. 解决字体显示异常的方法 #

从日志可见，Ghostscript找不到系统里的TimesNewRoman、Arial系列CID字体，只能用默认替代字体（比如Nimbus系列、DroidSansFallback），这些替代字体没有对应非标准字符的字形，导致显示异常。可通过以下方法解决：

• 方法一：安装缺失的字体文件
  把Times New Roman、Arial的完整TrueType字体包（包括常规、粗体、斜体等所有变体）安装到系统字体目录，或者直接复制到Ghostscript的字体资源目录（/usr/share/ghostscript/9.26/Resource/Font/）。安装完成后，Ghostscript就能找到对应字体，无需替换，非标准字符即可正常显示。

• 方法二：强制使用原PDF的嵌入字体
  如果原PDF已经嵌入了所需字体，添加参数让Ghostscript优先使用嵌入字体，不要去系统搜索缺失字体：

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dEmbedAllFonts=true -dSubsetFonts=false -sOutputFile=out.pdf in.pdf

• -dEmbedAllFonts=true：强制将所有字体嵌入到输出PDF

• -dSubsetFonts=false：禁止字体子集化，完整保留原字体的所有字符

• 方法三：指定自定义字体路径
  如果字体存放在非默认目录，用-sFONTPATH参数告诉Ghostscript字体位置：

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sFONTPATH=/path/to/your/font/folder -sOutputFile=out.pdf in.pdf

3. 复制原PDF嵌入字体到新PDF的方法 #

使用以下参数组合的Ghostscript命令，可完整保留原PDF中的嵌入字体：

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dEmbedAllFonts=true -dSubsetFonts=false -dPreserveCopyPage=true -sOutputFile=out.pdf in.pdf

• -dEmbedAllFonts=true：确保所有字体都嵌入到输出文件
• -dSubsetFonts=false：不做字体子集化，完整复制原嵌入字体的全部字符集
• -dPreserveCopyPage=true：尽可能保留原页面的资源结构，减少Ghostscript对字体的修改，最大程度还原原字体状态

内容的提问来源于stack exchange，提问作者JohnSmith