Attach or Insert Google Drive Files in Gmail

If you'd like to send a file in Gmail like a photograph or word document, you can either attach the file from your computer, or insert the file into your message using Google Drive.  (To insert files using Google Drive, you need to be using Gmail’s new compose and reply experience.)

Watch how to attach or insert a Google Drive File in Gmail:

Here's how to insert a file using Drive when you're composing a message:

1. Hover over the plus icon  at the bottom of the compose window, which will open the insert menu. (Remember, you need to be using Gmail's new compose and reply experience to insert files using Google Drive).
2. Click the Google Drive icon . In the window that appears, you can upload a file to Google Drive, as well as navigate to or search for files you've stored in Drive. For files stored in Drive, select the checkboxes next to the files you want to insert. 
    
3. Click the Insert button.  Gmail then adds a link to your message so recipients can click the link to view your file.

When you send the message, Gmail checks to see if your recipients have access to the file and will prompt you to adjust the sharing settings on the file(s) you've inserted, if needed.

Why should I insert using Drive instead of attaching a file?

• Send larger files:  When you're attaching files from your computer, you can only attach files up to 25 megabytes (MB) in size. By inserting files using Drive, you can send a file up to 10 gigabytes (GB).
• Simplify collaboration:  By inserting a document using Google Drive, you can avoid all that. Google Docs, Sheets, and Slides let you see each other’s edits and comments in real time and any changes collaborators make to the file are immediately visible to the people you’ve shared it with, so there’s no need to reattach new versions of the file and send them out again.
• Keep control over who sees your files:  Once you send an attachment, anybody can see it. Inserting files using Drive allows you to share files only with the people you want to share them with. You can delete the file or update the sharing settings on your file at any time. Learn more

Reference:  

• Google Gmail's Help: Insert files using Google Drive in Gmail
• Google Gooru: How to Attach Google Drive Files in Gmail
• Official Gmail Blog: Gmail and Drive - a new way to send files