Converting binary data to base64 in Google appscript - javascript

I'm getting an input data in appscript in the form of binary data (docx file data) which looks something like below
I need this data to be converted into Base64 string. I tried using Utilities class to encode it into base64, however, it returns a few character string which is invalid. Is there any way to convert this form of data in appscript?
The current script is as below
function run() {
var inputData = Eventbus.get('encodedData');//this is received as binary data
var convertedData = Utilities.base64Encode(inputData);//need to encode to base64 but doesn't work
Eventbus.set('decodedData',convertedData);
}
Thanks
Saurabh

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Then I can edit (or not) the json object. Then I can download it with JSON.stringify(json).
When I try to read or validate the output JSON I get errors signaling invalid characters, for example:
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What I need to do is best descriped as example.
Previously, I had the following code:
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