In an email you received, Gmail can preview common types (PDF, JPG, TXT, HEIC and more) in its own viewer, and nothing goes to Downloads. When a click still downloads, one of these is usually going on.

1. You are in compose, reply or forward

With no extension installed, clicking an attachment chip in compose or Forward makes Gmail download the file. There is no native preview there. To check a PDF or image before you send without downloading it, use Attachment Preview (below).

2. You clicked the download arrow

When you hover over an attachment card in a received email, Gmail shows a download icon. Click the middle of the card instead to open Gmail's preview.

3. Chrome is set to download PDFs

Go to chrome://settings/content/pdfDocuments and choose Open PDFs in Chrome. With Download PDFs selected, Chrome saves every PDF instead of showing it.

4. An extension is intercepting attachments

PDF tools such as the Adobe Acrobat extension can take over PDF clicks in Gmail and open a chrome-extension:// tab (or download). See Adobe Acrobat extension and Gmail PDFs for the exact Gmail checkbox to uncheck. Download managers and ad blockers can also change what happens; test in an Incognito window (extensions off by default).

5. That file type has no in-browser viewer for the path you used

Gmail's own viewer covers many Office types in received mail. Attachment Preview's Open in new tab only shows types Chrome can display (for example text). Word, Excel, PowerPoint and ZIP still download from that tab; for those, click the attachment card to use Gmail's viewer instead.

Preview in compose without downloading

Attachment Preview is a free Chrome extension that adds two buttons to Gmail attachments:

Preview on PDFs and images (PNG, JPG, GIF, WebP): opens the file in a viewer on top of Gmail. Nothing downloads.
Open in new tab on everything else: opens it in a tab where Chrome can display it (for example text files).

It works in opened emails and in compose, reply and forward, and it runs entirely in your browser.

Clean up what already downloaded

Open Chrome's downloads list (Ctrl+J), click Show in folder, and delete the copies you do not need.

Gmail attachments download instead of opening? Here's why and how to fix it