How do I know if I have damage from acid reflux disease?

Endoscopy. Upper endoscopy (egd) is the procedure of choice if you have had frequent acid reflux, indigestion or heartburn for more than 6 months. The egd allows detailed inspection of the lining of the esophagus for any inflammation or pre-cancerous changes (barrett's esophagus). Biopsies are often taken to differentiate these changes. After egd, proper treatment can be recommended.
Endoscopy. Acid reflux can lead to damage of the esophagus (swallowing tube) including strictures or even pre-cancerous changes. These changes are frequently only detected with endoscopy under the care of a skilled gastroenterologist.
Endoscopy. The primary way to assess/inspect the esophagus is esophagoscopy (upper endoscopy). This allows direct visual inspection. Other radiology "swallow studies" may provide suggestion of esophageal injury. But generally, those studies are not used primarily to look for gerd injury as much as to diagnose gerd and or other diseases.