How to use the utils.addStringToBuffer function in utils

copyBytesInto = (buffer: Uint8Array): Uint8Array => {
    this.validateDictionary();
    let remaining = this.dictionary.copyBytesInto(buffer);
    remaining = addStringToBuffer('\nstream\n', remaining);

    remaining.set(this.content, 0);
    remaining = remaining.subarray(this.content.length);

    remaining = addStringToBuffer('\nendstream', remaining);
    return remaining;
  };
}

private copyContentBytesInto = (buffer: Uint8Array): Uint8Array => {
    const remaining = addStringToBuffer(this.leadingIntegerPairsStr(), buffer);
    return this.objects.reduce(
      (remBytes, obj) =>
        addStringToBuffer('\n', obj.pdfObject.copyBytesInto(remBytes)),
      remaining,
    );
  };

copyBytesInto = (buffer: Uint8Array): Uint8Array => {
    let remaining = addStringToBuffer('BT\n', buffer);

    remaining = this.operators
      .filter(Boolean)
      .reduce(
        (remBytes: Uint8Array, op: PDFOperator) => op.copyBytesInto(remBytes),
        remaining,
      );

    remaining = addStringToBuffer('ET\n', remaining);
    return remaining;
  };
}

copyBytesInto = (buffer: Uint8Array): Uint8Array => {
    const remaining = addStringToBuffer(
      `%PDF-${this.major}.${this.minor}\n`,
      buffer,
    );
    remaining.set([charCode('%'), 130, 130, 130, 130, charCode('\n')], 0);
    return remaining.subarray(6);
  };
}

this.array.forEach((e, idx) => {
      if (e instanceof PDFIndirectObject) {
        remaining = addStringToBuffer(e.toReference(), remaining);
      } else if (e instanceof PDFObject) {
        remaining = e.copyBytesInto(remaining);
      } else {
        error(`Not a PDFObject: ${e}`);
      }
      remaining = addStringToBuffer(' ', remaining);
    });