Class MyActivity:

public void loadFormAsync(final String path) {
    AsyncTask<Void, Void, Void> openFormTask = new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... params) {
            openForm(path);
            return null;
        }

        @Override
        protected void onPostExecute(Void param) {
        }
    };
    openFormTask.execute();
}

public void loadForm(final Myform myForm) {
    pdfFile = new Document();
    byte[] pdfData = myForm.getPDFByteArray();

    try {
        int r = pdfFile.OpenMem(pdfData, null);
        if (r != 0) {
            throw new Exception("failed to load pdf");
        }

        pdfFile.SetCache( Global.tmp_path + "/temp.dat" );
        Global.def_view = 7;
        Global.render_mode = 2;
        Global.zoomLevel = 4.0f;

        Runnable runnable = new Runnable() {
            public void run() {
                pdfReader.PDFOpen(pdfFile, false, new VPDFListener(MyActivity.this));
                m_thumb.thumbOpen(pdfReader.PDFGetDoc(), new VThumbListener(pdfReader));
            }
        };
        MyActivity.this.runOnUiThread(runnable);

    } catch (Exception e) {
        e.printStackTrace();
    }
}

private void openForm(String path) {
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            closeForm();
            pdfReader = new VPDFReader(MyActivity.this,null);
        }
    };
    runOnUiThread(runnable);
    boolean opened = myApplication.openForm(path); // calling to class MyApplication
    Runnable runnable2 = new Runnable() {
        @Override
        public void run() {
            pdfLayer.addView(pdfReader);
        }
    };
    runOnUiThread(runnable2);
}

public void closeForm() {
    if (pdfReader != null) {
        pdfReader.PDFClose();
        pdfLayer.removeView(pdfReader);
    }
    pdfReader = null;
    pdfFile = null;
}

Class MyApplication:

public boolean openForm(String path) {
    MyForm myForm = readFileFromPath(path); // Some code to decode the file
    setForm(myForm);
    return true;
} 

public void setForm(MyForm myForm) {
    myActivity.loadForm(myForm);
}