Have you used the email to dropbox option in the latest dropbox version?

Hi symakhan, happy Monday! 

I'd be happy to answer some of your questions! 

In regards to eSignature, keep in mind that this feature allows you to create signable documents, add custom fields, and collect single and multi-party signatures from your visitors that are legally binding for both parties all while tracking your visitor’s engagement.

Here’s the relevant help article as to how you can Create Signable Documents with eSignature.

Moving on as to how Dropbox keeps your files safe, I believe that this Help Center article will cover it. However, if you have any questions that aren't mentioned in it, make sure to let me know! 

Concerning moving content from Dropbox to Google Drive: you can always download the files/folders you want locally, then upload them to Google Drive. How to download your content?You can either use our app, sync all the content locally, then create copies, and move them over to Google. 

Or you can use the website, download each folder individually and then move them over anywhere you might want. 

I hope I managed to answer some of your questions. If you have anything else, don't hesitate to let me know. I'll be leaving this thread open, so other users can also jump in and express their experiences, tips and tricks they have with Dropbox, or share their thoughts. 

I hope this helps!