Hello @fahabil698,

Firstly 

Locate the Attachment Use the sys_attachment table to find the file.

var attachmentGR = new GlideRecord('sys_attachment');
attachmentGR.addQuery('table_name', 'your_table_name'); // e.g., 'incident'
attachmentGR.addQuery('table_sys_id', 'your_record_sys_id');
attachmentGR.query();
if (attachmentGR.next()) {
var attachmentSysId = attachmentGR.getValue('sys_id');
}

Read Attachment Content Use the GlideSysAttachment API

var gsa = new GlideSysAttachment();
var fileContent = gsa.getContentStream(attachmentGR);
var reader = new GlideTextReader(fileContent);

var text = '';
var line;
while ((line = reader.readLine()) != null) {
text += line + '\n';
}
gs.info(text); // Or process the content as needed