Hi @dude_chill ,
As I understand you want to send a file from the documnet library on sharepoint that can be selected via a dropdown in powerapps and triggers a flow to send it.
Please refer to the screenshots below: 
In this, you can see that I have created a drop down and the data source is the Sharepoint Document Library (I created one by the name Pictures). And in the on change property of this I am triggering a flow that takes the "File Identifier" as a variable. 
In the flow you can see that we are using the file identifier from the powerapps to identify the file and get the content and passing that to the Outlook email.
If you want to send multiple files in a single run, create an array variable in flow and request input from powerapps. IN powerapps instead of the dropdown put a list where you can select multiple items at a time. In flow iterate through this array to get the files or use get files action an filter queries.
Hope this Helps!
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