Steps for downloading entire Ebook Central ebooks are somewhat complex and vary by device. ESTIMATED time to complete this process the first time: 15 minutes (subsequent downloads are easier).
Are you sure you need the entire book? If yes, then continue:
Downloading ProQuest Ebook Central electronic books usually requires downloading and installing the free Adobe Digital Editions for computers. For iOS and Android devices, download Adobe Digital Editions from the App Store or Google Play respectively.
One needs to also obtain an Adobe ID (set up a free Adobe Account) to access the ebook on more than 1 device.
ESTIMATED time to complete this process: 15 minutes.
Sign in 
For more detailed download instruction steps see the Ebook Central download guide.
Most ebooks can be downloaded for use for up to 21 days. After that period, the Adobe software disallows reading for that book.
When you download, choose the length of time from the options dropdown:
Q: If I download the full ebook, may I keep it permanently?
A: No.
Another option: you can download a PDF chapter from most ebooks. The PDF does not expire although you are expected to respect the copyright.
It is not currently possible to download an entire Ebook Central book to a Kindle device. However, one can download chapters and read them on a Kindle or other device capable of displaying PDF files. Note that some ebooks limit the number pages which can be downloaded.
Find a specific chapter in a book within Ebook Central and click "Download PDF Chapter". Or click the "Chapter Download" button
Remember where you have saved the PDF (which folder). Open up your email and attach the PDF you previously saved and prepare to send it to your Kindle account.
NOTE: this process will only work if the email from which you are sending it has been pre-authorized by you to send to your Kindle.
To approve the e-mail address from which you wish to send the PDF:
1. Visit Manage Your Content and Devices page.
2. Sign-in to Amazon account.
3. On the lower right, under Let Us Help you, visit "Manage Your Content and Devices" > Preferences, and scroll down to "Personal Document Settings" .
4. Under "Approved Personal Document E-mail List" click "Add a new approved e-mail address".
5. Enter your desired sending e-mail address to approve and select "Add Address."
6. Send the PDF document(s).
After sending the PDF, on your Kindle, go to Home > Menu >"Sync & Check for Items". Note that you will need to have WiFi turned ON.
More Amazon Kindle instructions for "Sending Documents to Your Kindle Library" are here:
https://www.amazon.com/gp/help/customer/display.html?nodeId=200767340#
Another option is to download the Send to Kindle app for your device on which you downloaded the PDF and use that to send the PDF to your Kindle.
Under Personal Document Settings > Send-to-Kindle E-Mail Settings in your Amazon account, you can see the email address (destination) for your Kindle device. Ensure that this is the email to which you are sending the PDF attachment of the ebook chapter.
screenshot
Ensure that the email from which you are sending the PDF is in the "Approved Personal Document E-mail List".
screenshot of what that looks like:
Total size of attached file needs to be 50 MB or less. It is possible to .ZIP a file to compress it and then send it.
If attempting to email a PDF of an ebook chapter to your @kindle.com account is problematic, still another method is to connect a USB cable to transfer files from the device upon which you have downloaded the e-book to your Kindle.