Issue Summary

`.pptx` files are OOXML packages (ZIP archives containing XML and media parts). Confluence inspects the internal structure of the archive to identify the file type and render the correct preview.

When a `.pptx` file is saved by a non-Microsoft application (e.g. LibreOffice Impress, online converters), the package places `[Content_Types].xml` as the first entry in the ZIP. Microsoft PowerPoint places `ppt/presentation.xml` first.

When `[Content_Types].xml` is the first entry, Confluence cannot disambiguate the file as a PowerPoint presentation and treats it as a generic ZIP archive (`application/zip`). No preview is generated, even though the file is a valid `.pptx` and Microsoft PowerPoint opens it without issue when downloaded.

Steps to Reproduce

1. Take any valid `.pptx` file produced by Microsoft PowerPoint.
2. Open it in LibreOffice Impress and use *Save As* → `.pptx`.
3. Upload the re-saved file to a Confluence Cloud page.
4. Click the file to view the preview.

Expected Results

The file is recognised as a Microsoft PowerPoint presentation and a slide preview is generated.

Actual Results

The file is treated as a generic archive. No preview is generated; the file viewer displays a generic archive download card instead of slide content.

The misidentification can be confirmed locally:

``
$ file --brief --mime-type re-saved.pptx
application/octet-stream

$ file --brief --mime-type original-from-powerpoint.pptx
application/vnd.openxmlformats-officedocument.presentationml.presentation
​```

The differing internal ZIP layout:

​```
$ unzip -l affected.pptx | head -5
  Length      Date    Time    Name
---------  ---------- -----   ----
    13451  01-01-1980 00:00   [Content_Types].xml      <-- first entry
      885  01-01-1980 00:00   _rels/.rels

$ unzip -l working.pptx | head -5
  Length      Date    Time    Name
---------  ---------- -----   ----
     4217  01-01-1980 00:00   ppt/presentation.xml    <-- first entry
      219  01-01-1980 00:00   customXml/item1.xml
​```

Workaround

Open the affected file in *Microsoft PowerPoint* (Desktop or Microsoft 365 web), use *File → Save As* to save a fresh copy, and upload that copy to Confluence. Microsoft PowerPoint re-saves the package in a layout Confluence correctly identifies as a PowerPoint presentation.

Renaming or re-uploading the file without re-saving in Microsoft PowerPoint does *not* resolve the issue, because the internal archive layout is unchanged.