Short answer: if Gmail's preview works for you and you only read attachments you receive, you may not need anything else. Attachment Preview is for checking files in compose before you send (where Gmail downloads), for staying in the thread with an overlay and page counter, and for long PDFs.
Side by side
| Gmail's built-in preview | Attachment Preview 1.1 | |
|---|---|---|
| Price | Free, built in | Free extension |
| Opened emails | Yes (PDF, JPG, TXT, HEIC and more; nothing to Downloads) | Yes |
| Compose, reply, forward | No (chip click downloads) | Yes, Preview button on attached PDFs and images |
| PDFs | Yes | Yes, built-in pdf.js viewer, select and copy text, page counter |
| Password-protected PDFs | Yes, prompts for a password | Yes (version 1.1 and later): Password form in the overlay; you stay in the thread |
| Images | Yes (including HEIC) | PNG, JPG, GIF, WebP (not HEIC in Preview) |
| Word, Excel, PowerPoint | Yes, Gmail's viewer | No (Open in new tab downloads them) |
| Other types | Some | Open in new tab, shown if Chrome can display them |
| Layout | Full-screen viewer | Overlay over your inbox; Esc returns you |
| Where the file goes | Shown by Google's viewer | Loaded from Gmail with your session and shown in your browser only |
| With Adobe Acrobat installed | Native PDF click opens a chrome-extension tab | Preview still opens normally |
| Mobile apps | Yes | No, desktop Chrome and Chromebook only |
| Install needed | No | Yes, Chrome Web Store |
When Gmail's preview is enough
- You read attachments you receive, mostly Office files or HEIC photos.
- You use Gmail on your phone as much as your computer.
- You rarely need to check a file in compose before sending.
When Attachment Preview helps
- You want to check a PDF or image in your draft before sending it, without Gmail downloading the chip click.
- You want an overlay that keeps you in the thread, with a page counter, instead of Gmail's full-screen viewer.
- You open long PDFs and want scrolling that stays fast.
- Acrobat is installed and you still want a one-click Preview that is not taken over.
Questions
Does Attachment Preview replace Gmail's preview?
No. Gmail's preview keeps working. The extension adds its own Preview and Open in new tab buttons next to attachments.
What about password-protected PDFs?
Gmail's native viewer prompts for a password, and so does Attachment Preview in version 1.1 and later. The difference is that Attachment Preview keeps you in the overlay on top of your inbox. The password is used only to open that file and is never stored, logged or transmitted.
Does it send my attachments anywhere?
No. It loads the attachment you clicked from Gmail, using your own sign-in, and shows it in your browser. It has no servers, no analytics and no account. Privacy policy.
Does it work with Outlook or Yahoo Mail?
No. Gmail on the web in Chrome only.
Related: How to preview an attachment in Gmail · Preview attachments before sending · Gmail PDF preview not working