how to free memory used by pdf2json?

I have a server that run four process to handler client side pdf.
I found that when client side send a 10mb pdf file, one process will used 400mb memory and never free it.
When run it for long time and receive some big pdf, it will take me about 4gb memory, and make other app down.
I have a test code like this

const pdfParser = new PDFParser(this, 1);

pdfParser.on('pdfParser_dataReady', pdfData => {
    console.log('--------------raw-----------------');
    console.log(pdfParser.getRawTextContent());
});

pdfParser.loadPDF('/Users/saye/Downloads/Gradle_Recipes_for_Android.pdf');
let server = http.createServer((req, res) => {
    res.write('hello');
    res.end();
});
server.listen(2345);

so what should I do to make memory free

Start by reproducing the memory growth with the shown PDFParser example and the referenced Gradle_Recipes_for_Android.pdf file, then observe memory across repeated calls to loadPDF and pdfParser_dataReady. Done means the cause of retained memory is identified and memory is reclaimed after processing, with the behavior verified under repeated large-PDF requests.