How to connect 2 forms in drupal 7?
You might need MultiStep form using ajax enabled. Just implement #ajax on the buttons of form as in the given link.

    $form['buttons'] = array(
      '#type' =&gt; 'container',
    );
    if($form_state['step'] !== 1) {
      $form['buttons']['back'] = array(
        '#type' =&gt; 'submit',
        '#value' =&gt; t('Back'),
        '#limit_validation_errors' =&gt; array(),
        '#submit' =&gt; array('ajax_form_multistep_form_back_submit'),
        '#ajax' =&gt; array(
          // We pass in the wrapper we created at the start of the form
          'wrapper' =&gt; 'ajax_form_multistep_form',
          // We pass a callback function we will use later to render the form for the user
          'callback' =&gt; 'ajax_form_multistep_form_ajax_callback',
        ),
      );
    }
    if($form_state['step'] !== 3) {
      $form['buttons']['forward'] = array(
        '#type' =&gt; 'submit',
        '#value' =&gt; t('Next'),
        '#ajax' =&gt; array(
          'wrapper' =&gt; 'ajax_form_multistep_form',
          'callback' =&gt; 'ajax_form_multistep_form_ajax_callback',
        ),
      );
    }
    else {
      $form['buttons']['submit'] = array(
        '#type' =&gt; 'submit',
        '#value' =&gt; t('Submit'),
        '#ajax' =&gt; array(
          'wrapper' =&gt; 'ajax_form_multistep_form',
          'callback' =&gt; 'ajax_form_multistep_form_ajax_callback',
        ),
      );
    }