According to Google's blog, a file generated in a chat can be expanded to full screen to type edits directly, a passage can be highlighted to ask a question about it, or Gemini can be asked to rewrite text and change visual elements. Supported types include Google Docs, Google Sheets, slide decks, Markdown and TXT files, code and PDFs.
PDF preview and editing work on the web and on mobile; the other formats are supported on the web only for now. As an example, Google shows a PDF study guide created from handwritten lecture notes uploaded to the chat, then edited by hand and queried about its content.
The announcement does not say whether limits differ by subscription tier, or whether files can be saved directly to Drive or exported to other formats.