Webhook to copy record with file attachment from one table to another (No Pipelines)

Hello,

I've been trying to figure this one out, and I'm a little new with Webhooks, so bear with me.

A little background, I have a main app with projects, and I set up a Pipeline to copy a template of a "project app" for a specific project that can be customized and tailored to that single project while still syncing certain fields with the main app.

One of the tables in this newly-created project app is an Attachments table. I want to set up a Webhook so that whenever records in this table (which have file attachments) are added, they are copied to the main app's Attachments table. 

I know there is a simple way of doing this in Pipelines. However, the problem is that I would have to create a new Pipeline for each project app because the triggering event would be from an unknown app until it's created. I wouldn't have this problem with a Webhook since the Webhook would be copied and just needs to be activated. I just don't know how to get a Webhook to do what I want it to do. I know I can create records with an API, but I would need the Base64 encoded content of the file attachment, and I don't know how to retrieve that. 

Any assistance would be greatly appreciated. Thank you!

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Brian
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