1. Open the mail app on your iPad (this example shows the iOS Mail app, but Gmail, etc. also work).
2. Go to the email that has the attachment. Click on the attachment to download. Once it's done downloading, click on it again.
3. Press the "Share" icon in the upper right corner.
4. Select "Save to Markup."
5. Select to "Keep in original" or "Save to PDF."
6. Once you have selected, the conversion to Markup will begin. This process may take a few moments; the attachment will be available in the "Extension" folder in the Markup app.