我是 Linux 系统的新用户（我正在使用 Lubuntu 18.04 LTS），我还在学习英语，如果我犯了错误，请见谅
我无法打开 PDF 文档。当我尝试打开我的默认阅读器 (Okular) 时，它无法再显示我最常用的某些“.pdf”文档...最近我升级了一些软件包，之后 pdf 阅读器就无法正常工作了。我安装的所有阅读器 (Okular、Evince、Atril) 都出现了相同的错误警告。
这是我在终端中收到的错误警告：
$ okular
(okular:8965): Gtk-WARNING **: 23:28:29.044: Theme parsing error: gtk.css:597:14: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.044: Theme parsing error: gtk.css:597:14: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.044: Theme parsing error: gtk.css:600:17: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.046: Theme parsing error: gtk.css:784:14: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.047: Theme parsing error: gtk.css:784:14: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.047: Theme parsing error: gtk.css:787:17: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.050: Theme parsing error: gtk.css:1096:14: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.050: Theme parsing error: gtk.css:1096:14: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.050: Theme parsing error: gtk.css:1099:17: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.060: Theme parsing error: gtk.css:2286:8: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.060: Theme parsing error: gtk.css:2286:18: Using Pango syntax for the font: style property is deprecated; please use CSS syntax
(okular:8965): Gtk-WARNING **: 23:28:29.061: Theme parsing error: gtk.css:2291:8: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.061: Theme parsing error: gtk.css:2291:18: Using Pango syntax for the font: style property is deprecated; please use CSS syntax
(okular:8965): Gtk-WARNING **: 23:28:29.071: Theme parsing error: gtk.css:4357:14: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.071: Theme parsing error: gtk.css:4357:14: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4419:12: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4419:12: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4428:16: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4428:16: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4443:22: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4443:22: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4499:12: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4501:16: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.072: Theme parsing error: gtk.css:4501:16: Expected a string.
(okular:8965): Gtk-WARNING **: 23:28:29.073: Theme parsing error: gtk.css:4549:12: not a number
(okular:8965): Gtk-WARNING **: 23:28:29.073: Theme parsing error: gtk.css:4549:12: Expected a string.
QApplication: invalid style override passed, ignoring it.
Segmentation Fault (core dumped) #(This part was in Portuguese, maybe in English it was different?)
Gtk-WARNINGS 很常见，并且不会影响程序的可用性，但是“分段错误（记录的核心映像）”是不正常的。
你能帮我解决这个问题吗？
最近升级的软件包是：
2018-12-03 10:06:38 upgrade numix-icon-theme:all 0.3+933~201809192203~ubuntu18.04.1 0.3+934~201812011102~ubuntu18.04.1
2018-12-03 10:06:51 upgrade numix-icon-theme-square:all 18.10.03+201810041547~ubuntu18.04.1 18.12.01+201812011517~ubuntu18.04.1
2018-12-03 14:30:08 upgrade linux-generic:i386 4.15.0.39.41 4.15.0.42.44
2018-12-03 14:30:09 upgrade linux-image-generic:i386 4.15.0.39.41 4.15.0.42.44
2018-12-03 14:30:19 upgrade linux-headers-generic:i386 4.15.0.39.41 4.15.0.42.44
2018-12-03 14:30:20 upgrade linux-libc-dev:i386 4.15.0-39.42 4.15.0-42.45
2018-12-04 11:04:18 upgrade libperl5.26:i386 5.26.1-6ubuntu0.2 5.26.1-6ubuntu0.3
2018-12-04 11:04:20 upgrade perl:i386 5.26.1-6ubuntu0.2 5.26.1-6ubuntu0.3
2018-12-04 11:04:21 upgrade perl-base:i386 5.26.1-6ubuntu0.2 5.26.1-6ubuntu0.3
2018-12-04 11:04:23 upgrade perl-modules-5.26:all 5.26.1-6ubuntu0.2 5.26.1-6ubuntu0.3
2018-12-04 11:04:25 upgrade libfwupd2:i386 1.0.6-2 1.0.9-0ubuntu2
2018-12-04 11:04:26 upgrade fwupd:i386 1.0.6-2 1.0.9-0ubuntu2
2018-12-04 11:04:32 upgrade libpoppler-qt5-1:i386 0.62.0-2ubuntu2.2 0.62.0-2ubuntu2.4
2018-12-04 11:04:33 upgrade poppler-utils:i386 0.62.0-2ubuntu2.2 0.62.0-2ubuntu2.4
2018-12-04 11:04:34 upgrade libpoppler-glib8:i386 0.62.0-2ubuntu2.2 0.62.0-2ubuntu2.4
2018-12-04 11:04:35 upgrade libpoppler73:i386 0.62.0-2ubuntu2.2 0.62.0-2ubuntu2.4
2018-12-04 11:04:36 upgrade syncthing:i386 0.14.52 0.14.53
2018-12-04 22:52:41 upgrade chromium-browser-l10n:all 70.0.3538.77-0ubuntu0.18.04.1 70.0.3538.110-0ubuntu0.18.04.1
2018-12-04 22:52:43 upgrade chromium-browser:i386 70.0.3538.77-0ubuntu0.18.04.1 70.0.3538.110-0ubuntu0.18.04.1
2018-12-04 22:52:54 upgrade chromium-codecs-ffmpeg-extra:i386 70.0.3538.77-0ubuntu0.18.04.1 70.0.3538.110-0ubuntu0.18.04.1
我认为 perl、poppler 及其库是导致问题的软件包。我之所以这么说，是因为在这些更新之后，我再也无法打开 pdf
我仍然可以打开电脑上的一些 PDF，但不是全部（不幸的是，我的最重要的文件也遇到了这个问题）
提前感谢您的关注