You or your client can can add attachments to questions in the Client Portal. If your client uploads an attachment to a transaction question, you can also push this directly to QuickBooks to the transaction (e.g., for a receipt) or Payee (e.g., for a W9).
If you see that a client has uploaded an attachment, scroll to the right-hand side of your screen and click the attachments icon. To preview the attachment, just click its name.
And to upload the file to QBO, click Upload to Transaction or Upload to Vendor.
You can also use non-transaction questions to request statements, which your clients can upload to their client portal as well. For more on this, see Recurring Questions.