The below image is an example of the steps that are required. You can add any destination step to the flow. I added a Run File step to view the pdf document after the conversion before it is sent to a destination.
In the return statement in the Calculator step below, the pdf file is being converted to a Base64 file.
Copy and paste the below code in the Calculator step:
let inputRecord=input.record;
return createBuffer(inputRecord.PDF_Data_String_1__c,‘base64’);