In Dynamics 365 Portal we can make entity form able to attach files. For this we need to go to the Add Attach File section in the Additional Settings tab of Entity Form as shown in the following screen shot.
For e.g. in the below Contact Us form, we have checked Attach File check box which add
the File attachment control to the web page.
Attach File Save Option: Place where it will store files as an attachment. Here its set to Notes.
Allow Multiple Files: Allows user to attach multiple files
Label: Shows the text to instriuct user to attach a file.
Attach File Required: This option makes attaching a file mandatory and the Required
Required Error Messgae: It shows the associated error message.
Attach File Required: This option makes attaching a file mandatory and the required
Restrict Files to Accepted Types: Allows only specifiec files to be attached.
Files Type Error Message: Shows error message when try to attach a file which file type is not allowed to attach.
Files Size Error Message:Shows error message when try to attach a file more than the size limit set.
Now check the Contact Us form in portal at the end user view.
Now try to Click on Submit without attaching a file
Now try to attach multiple files and submit by entering all mandatory fields.