Sending pdf as binary in POST request (from Javascript)

I want:

To send a file (I have my eye on .docx and text files, but let's use a .pdf as an example) as binary in the body of a POST request from a browser (Javascript).

Main problem

I can do this just fine in POSTMAN. You can select "binary" as the body type, and viola! your file is configured to be the body. But I don't know how to mimic that behavior in Javascript.

My question is: On the client-side, in Javascript, how can I get a file into my POST request as binary?

Specifically, how can I get the file into the same format that POSTMAN uses when you select Body -> Binary in a POST request?

For context: I have been using this guide to get everything configured how I want in AWS. It ends with making requests in POSTMAN. But adding a file as binary in POSTMAN is one thing - doing it from a browser in Javascript is another, and the main question that I have.

I am sending this through API Gateway to a Lambda function. I have API Gateway configured to handle application/pdf as binary, and the Lambda function to decode it once it arrives.

So I think I want to hand it in as a binary blob, not base64. But not sure exactly how.

JavaScript

postBinary() {
                  var settings = {
                      "url": "https:<my-aws-api>.amazonaws.com/v1/upload",
                      "method": "POST",
                      "timeout": 0,
                      "headers": {
                        "Content-Type": "application/pdf"
                      },
                       "data": <my pdf file here as binary>
                    };

                    $.ajax(settings).done(function (response) {
                      console.log(response);
                    });
           },

API Gateway:

Integration has 'When there are no templates defined (recommended)' set to 'Content-Type':'application/pdf'. The API's Binary Media Types have 'application/pdf' set. I know I have CORS set correctly - I can pass strings through the POST request and get success messages back, but I would like to handle files here, not just a simple string. I also want to avoid requiring the client side to parse out data on their end.

My Lambda function will take the file and then parse information out of it, then send it back.

Lambda function:

import json
import base64
import boto3
BUCKET_NAME = 'my-bucket'
def lambda_handler(event, context):
    file_content = base64.b64decode(event['content'])
    
    parsed_data = some_function(file_content) # parse information from file

    return {
        'statusCode': 200,
        'body': {
            'file_path': file_path
        }
    }

In the end, we want a user experience of: choose a file, send to API, get back parsed data. Simple.

Note: I know there are lots of good reasons to put files in s3 instead of going through Lambda first. But our files are small, and we are not concerned about taking considerable compute time/power in Lambda. Further, we want to avoid sending to s3 right away because we would like the user to only have to make one call to the API: send file in POST request, get results. If we send to s3 first, the user has to send multiple requests: request pre-signed URL, send file to s3, request results from parsing.

I am mostly concerned with the fact that this is possible in POSTMAN and it must be possible via browser/Javascript as well.

Thanks, everyone!