Shopify's Request a Quote feature allows customers to upload a file, which will seamlessly transfer to QuoteMachine. Here's how:

To begin, you will need to add a 'File' custom field. You can do this by navigating to Sales Tools > Custom Fields > + Add Custom Field.
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From here, choose the custom field name, in this example I choose Upload a File. From here, make sure the the custom field is available from Quotes, and now choose your Field type, which will be File. Click Save custom field.

After creating your custom field, the next step is to integrate it into your Request a Quote form.

Click Ecommerce Configuration > Quote Form > Add a Form Component. From here, select the custom field you just created. Click Save Form Configuration.

You'll now find this custom field in your Request a Quote form within Shopify.

After the customer submits a Quote Request and uploads a file(s), you can locate your new quote request and view the uploaded file.

To learn how to use the Request a Quote Form, please visit this article: Using the Shopify Request a Quote form