You can attach external files to the form you are creating if its form settings allow so. Below are the steps to attach an external file while creating a new form:

1. Follow the steps to create a form.

2. Click on attachment icon at top right (available based on relevant form settings configuration) to upload attachments (external files) onto the new form.

Similarly, the option to upload attachments (external files) will also be available while replying to an form as shown in below screenshot.

Based on form settings configuration, the option to attach an external file can be available while editing an existing form as well.

3. It will open a popup wherein you will get option to upload files using drag and drop.

4. Files selected using drag and drop functionality will appear as shown below:

When not using drag and drop, click on 'Select Files' to browse for the external files from your local system.

Once done with selecting files, click 'Attach' to complete uploading of selected files.