Amazon gives you a personalized kindle email id. Check for it in your amazon kindle cloud reader after logging in through amazon.com in your internet browser.
After logging in: Go to the settings page in amazon kindle cloud reader section (look for it under My Account --> Manage your Devices)
The URL is something like this:
https://www.amazon.com/mn/dcw/myx.html#/home/settings/payment
Scroll to the bottom. You will see a section named:
Send-to-Kindle E-Mail Settings
You can e-mail personal documents to the following Kindle(s) using the e-mail addresses shown.
Under it, you will see your own personal kindle.com email id.
Now, one more step.
Scroll further down. You will see a link:
Add a new approved e-mail address
Ensure that you authorise Amazon Kindle Cloud Reader to receive your PDFs through your personal gmail or email id.
Once authorised, you are ready to move PDFs to your account.
Login to your gmail / email account in your email client/browser. Send your pdf as attachment to your personalised kindle email id.
DONE. Your ebook should appear in about five minutes automatically in your Kindle for PC (or synch it to download) or Kindle handheld or any other Kindle reader.
Hope this helps.