As the duplicate only suggest what can be done, following is more helpful:
To create a multi file attachment control in InfoPath, you can make
use of a Repeating
that has a File Attachment as one of its fields.
Perform the following steps to create a multi-file attachment in
Add a Repeating Table with 1 column to your InfoPath form template.
Go to the Data Source task pane and double-click the field under the repeating node for the Repeating Table.
Change the Data type to Picture or File Attachment (base 64) and click OK.
Right-click the field in the Repeating Table on the InfoPath form template, and select Change To, and then File Attachment
from the context menu that appears.
That is how you can attach multiple files in InfoPath.
Top 10 questions about InfoPath attachments