Content of PDF files comes out scambled

[ArDevKarl]

Describe the bug
I'm trying to generate a simple PDF of my API, without any styles/template. THe resulting pdf looks all scambled:

To Reproduce
My docfx.json:

{
  "metadata": [
    {
      "src": [
        {
          "src": "./..",
          "files": [
            "Assembly-CSharp.csproj"
          ]
        }
      ],
      "dest": "api",
      "disableGitFeatures": false,
      "disableDefaultFilter": false,
      "filter": "filterConfig.yml"
    }
  ],
  "build": {
     "globalMetadata": {
      "pdf": true,
      "pdfTocPage": true
    },    
    "content": [
      {
        "files": [
          "api/**.yml",
          "api/index.md"
        ]
      },
      {
        "files": [
          "toc.yml",
          "*.md"
        ]
      }
    ],
    "overwrite": [
      {
        "files": [
          "apidoc/**.md"
        ],
        "exclude": [
          "obj/**",
          "_site/**"
        ]
      }
    ],
    "dest": "_site",
    "globalMetadataFiles": [],
    "fileMetadataFiles": [],
    "postProcessors": [],
    "markdownEngineName": "markdig",
    "noLangKeyword": false,
    "keepFileLink": false,
    "cleanupCacheHistory": false,
    "disableGitFeatures": false
  }
}

Expected behavior
A PDF file with readable content without any styling

Context (please complete the following information):

• OS: Windows 11
• Docfx version: 2.76.0

Is this a bug or is it mandetory, to add styling?

[filzrev]

without any styles/template.

When template is not specified. default template is used as fallback value.

It seems same problems that are reported at (#9653)

---

I can also reproduce problem on my environment (Windows 11)
with following steps.

1. Edit docfx official docs docfx.json to use default template only
2. Run docfx build command
3. Run docfx pdf command
4. Following warnings displayed. and PDF content is corrupted.

warning: Timeout waiting for page to load, generated PDF page may be incomplete: http://127.0.0.1:59028/docfx-cli-reference/docfx.html
warning: Timeout waiting for page to load, generated PDF page may be incomplete: http://127.0.0.1:59028/docfx-cli-reference/docfx.html

And it can't be resolved with DOCFX_PDF_TIMEOUT settings.

It seems there is problem in docfx-cli-reference/docfx.md content.
And it can also reproduce problems with following minimum markdown/yml file.

sample.md

# docfx

toc.yml

- name: Sample
  href: sample.md

[filzrev]

For docfx heading element problems.
It seems be occurred by following logics.
https://github.com/dotnet/docfx/blob/b7285fcdfb04e6f4132d702217588de6236bfa4c/src/Docfx.App/PdfBuilder.cs#L161C1-L161C92

It's not completed if docfx ID element exists (and docfx.ready variable is not set when using default template)

---

For wrong PDF content generated problem.
It seems currently not supported usage. (As discussed at #9393)
And Create PDF Files document have following note exists.

This article applies to docfx 2.73.0 or greater and the modern site template.