Yes, using the Enable File Upload Feature you can provide the file upload option to clients on the form. You can get a detailed description of this feature in the following doc - Configuration Guide for Enable File Upload Feature.
P.S. Discover Update Client Details, the easy way to keep client information up to date in Salesforce. Find it on AppExchange - https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3A00000EcsATUAZ