Rejection reasons

Reason	When
empty	The file has no bytes.
too-large	The file is larger than maxBytes.
type-not-allowed	The extension is not supported, or not in allowedExtensions (which by default holds only low-risk formats).
mime-mismatch	The declared MIME type does not belong to the extension. An empty type, application/octet-stream and application/zip are accepted for every extension.
content-mismatch	The bytes are not what the extension says, or cannot be read: a wrong signature, a zip bomb, a malformed ZIP or OLE file, a broken media file, an image sequence, binary data in a text file, or a file inside an archive that is of a format not in your list, another archive, a link or at an unsafe path.
macros	The file carries active content. See below.
encrypted	The file is password-protected, so its content cannot be checked.

The checks run in this order, so a file that is too large is refused as too-large before its bytes are read.

What macros covers

The name is short for all active content:

• VBA projects and ActiveX controls in Office files
• Excel 4.0 macro sheets
• Embedded and linked OLE objects
• DDE fields and links
• altChunk imports, subdocuments, frames and remote templates
• Basic and script modules, event listeners and macro links in OpenDocument files
• JavaScript, launch, submit and import actions, links to other files, multimedia, XFA forms and attachments in PDFs
• Formulas that call a function or DDE in CSV files
• Objects, templates and DDE fields in RTF files
• Any of the above in a file inside an archive

The per-format pages list the details: PDF, Office, OpenDocument, CSV.