Can I upload a document to an Issue in github?

Yes. Search for:

<span
  data-component="text"
  class="prc-Button-Label-pTQ3x"
> Paste, drop, or click to add files </span>

This shall invoke <input type="file">.

I have a document that I would like to reference from a github issue, but there is not a way to upload it. Any ideas?

Unfortunately, its Accept header is */*, which means that all file upload type validation occurs server-side.

If you upload an impermissible file type (say, .pak), you shall see:

File type not allowed: .pak

However, this occurs after file upload. To avoid this, GitHub luckily documents its upload restrictions:

Types ^[1]

We support these files:

• PNG (.png)

• GIF (.gif)

• JPEG (.jpg, .jpeg)

• SVG (.svg)

• Log files (.log)

• Markdown files (.md)

• Microsoft Word (.docx), PowerPoint (.pptx), and Excel (.xlsx) documents

• Text files (.txt)

• Patch files (.patch)

  If you use Linux and try to upload a .patch file, you will receive an error message. This is a known issue.

• PDFs (.pdf)

• ZIP (.zip, .gz, .tgz)

• Video (.mp4, .mov, .webm)

Sizes ^[2]

The maximum file size is:

• 10MB for images and gifs
• 10MB for videos uploaded to a repository owned by a user or organization on a free plan
• 100MB for videos uploaded to a repository owned by a user or organization on a paid plan
• 100MB for videos
• 25MB for all other files