diff --git a/docs/user/guides/pdf-non-ascii-languages.rst b/docs/user/guides/pdf-non-ascii-languages.rst
index f05bee5aff8..b181c571a29 100644
--- a/docs/user/guides/pdf-non-ascii-languages.rst
+++ b/docs/user/guides/pdf-non-ascii-languages.rst
@@ -3,8 +3,6 @@ Sphinx PDFs with Unicode
 
 Sphinx offers different `LaTeX engines`_ that have better support for Unicode characters
 and non-European languages like Japanese or Chinese.
-By default Sphinx uses ``pdflatex``,
-which does not have good support for Unicode characters and may make the PDF builder fail.
 
 .. _LaTeX engines: http://www.sphinx-doc.org/en/master/usage/configuration.html#confval-latex_engine
 
@@ -17,7 +15,7 @@ to modify Sphinx and Read the Docs behavior to make your documentation to build
 
 For docs that are not written in Chinese or Japanese,
 and if your build fails from a Unicode error,
-then try ``xelatex`` as the ``latex_engine`` instead of the default ``pdflatex`` in your ``conf.py``:
+then try ``xelatex`` as the ``latex_engine`` in your ``conf.py``:
 
 .. code-block:: python
 
diff --git a/readthedocs/doc_builder/backends/sphinx.py b/readthedocs/doc_builder/backends/sphinx.py
index 803e14b7fb4..22d1ddb22c3 100644
--- a/readthedocs/doc_builder/backends/sphinx.py
+++ b/readthedocs/doc_builder/backends/sphinx.py
@@ -336,38 +336,6 @@ def sphinx_parallel_arg(self):
             return ['-j', 'auto']
         return []
 
-    def venv_sphinx_supports_latexmk(self):
-        """
-        Check if ``sphinx`` from the user's venv supports ``latexmk``.
-
-        If the version of ``sphinx`` is greater or equal to 1.6.1 it returns
-        ``True`` and ``False`` otherwise.
-
-        See: https://www.sphinx-doc.org/en/master/changes.html#release-1-6-1-released-may-16-2017
-        """
-
-        command = [
-            self.python_env.venv_bin(filename='python'),
-            '-c',
-            (
-                '"'
-                'import sys; '
-                'import sphinx; '
-                'sys.exit(0 if sphinx.version_info >= (1, 6, 1) else 1)'
-                '"'
-            ),
-        ]
-
-        cmd_ret = self.run(
-            *command,
-            bin_path=self.python_env.venv_bin(),
-            cwd=self.project_path,
-            escape_command=False,  # used on DockerBuildCommand
-            shell=True,  # used on BuildCommand
-            record=False,
-        )
-        return cmd_ret.exit_code == 0
-
 
 class HtmlBuilder(BaseSphinx):
     relative_output_dir = "_readthedocs/html"
@@ -548,12 +516,7 @@ def build(self):
             raise BuildUserError("No TeX files were found.")
 
         # Run LaTeX -> PDF conversions
-        # Build PDF with ``latexmk`` if Sphinx supports it, otherwise fallback
-        # to ``pdflatex`` to support old versions
-        if self.venv_sphinx_supports_latexmk():
-            success = self._build_latexmk(self.project_path)
-        else:
-            success = self._build_pdflatex(tex_files)
+        success = self._build_latexmk(self.project_path)
 
         self._post_build()
         return success
@@ -625,59 +588,6 @@ def _build_latexmk(self, cwd):
 
         return cmd_ret.successful
 
-    def _build_pdflatex(self, tex_files):
-        pdflatex_cmds = [
-            ['pdflatex', '-interaction=nonstopmode', tex_file]
-            for tex_file in tex_files
-        ]  # yapf: disable
-        makeindex_cmds = [
-            [
-                "makeindex",
-                "-s",
-                "python.ist",
-                "{}.idx".format(
-                    os.path.splitext(
-                        os.path.relpath(tex_file, self.absolute_output_dir)
-                    )[0],
-                ),
-            ]
-            for tex_file in tex_files
-        ]  # yapf: disable
-
-        if self.build_env.command_class == DockerBuildCommand:
-            latex_class = DockerLatexBuildCommand
-        else:
-            latex_class = LatexBuildCommand
-        pdf_commands = []
-        for cmd in pdflatex_cmds:
-            cmd_ret = self.build_env.run_command_class(
-                cls=latex_class,
-                cmd=cmd,
-                cwd=self.absolute_output_dir,
-                warn_only=True,
-            )
-            pdf_commands.append(cmd_ret)
-        for cmd in makeindex_cmds:
-            cmd_ret = self.build_env.run_command_class(
-                cls=latex_class,
-                cmd=cmd,
-                cwd=self.absolute_output_dir,
-                warn_only=True,
-            )
-            pdf_commands.append(cmd_ret)
-        for cmd in pdflatex_cmds:
-            cmd_ret = self.build_env.run_command_class(
-                cls=latex_class,
-                cmd=cmd,
-                cwd=self.absolute_output_dir,
-                warn_only=True,
-            )
-            pdf_match = PDF_RE.search(cmd_ret.output)
-            if pdf_match:
-                self.pdf_file_name = pdf_match.group(1).strip()
-            pdf_commands.append(cmd_ret)
-        return all(cmd.successful for cmd in pdf_commands)
-
     def _post_build(self):
         """Internal post build to cleanup PDF output directory and leave only one .pdf file."""
 
diff --git a/readthedocs/projects/tests/test_build_tasks.py b/readthedocs/projects/tests/test_build_tasks.py
index 9eb7f4e5915..9245f2876fa 100644
--- a/readthedocs/projects/tests/test_build_tasks.py
+++ b/readthedocs/projects/tests/test_build_tasks.py
@@ -719,18 +719,9 @@ def test_build_commands_executed(
                     cwd=mock.ANY,
                     bin_path=mock.ANY,
                 ),
+                mock.call("cat", "latexmkrc", cwd=mock.ANY),
                 # NOTE: pdf `mv` commands and others are not here because the
                 # PDF resulting file is not found in the process (`_post_build`)
-                mock.call(
-                    mock.ANY,
-                    "-c",
-                    '"import sys; import sphinx; sys.exit(0 if sphinx.version_info >= (1, 6, 1) else 1)"',
-                    bin_path=mock.ANY,
-                    cwd=mock.ANY,
-                    escape_command=False,
-                    shell=True,
-                    record=False,
-                ),
                 mock.call(
                     mock.ANY,
                     "-m",