How can we export the complete custom report page with the charts and bars to a pdf or any other format?

Custom reports provide a "csv" download option. If you need the same presentation of data including charts then you use the browser feature or a plugin to export in required format.

An alternative is to use the Analytics API to get data and use external reporting tools.

http://docs.apigee.com/analytics-services/content/use-analytics-api-measure-api-program-performance

The Data you can get in JSON format via the stats APIs, which are documented.

As for getting a VIEW of the data, I don't have any easy solutions.

I have some ideas. They require some effort on your part.

1. Export the data in json format, convert to CSV, then produce an Excel chart or Google Sheet with your desired chart. This requires programming to the Excel or Google Sheets APIs. An example of this is available here: https://github.com/DinoChiesa/ApigeeEdge-API-Traffic-Summarizer
2. use selenium to automate the Apigee Admin UI to export the charts you desire.
   I have produced a proof-of-concept of this. https://github.com/DinoChiesa/Java-Selenium-EdgeDashboardSnapper . It works "unattanded": you could have the thing run every morning at 7:00am if you want, configured as a cron job. This tool exports UI only, not actual data. This isn't a general solution. To make this work for "any chart", you would have to crack open the code and extend it.