Hi Leaston,
You only get charged if you receive the documents via 3G rather than WIFI. To prevent receiving documents you email via 3G you can:
1) Go to the Manage Your Kindle page in the Amazon Kindle store and alter your personal limit to 0.00 - that will ensure you never get charged and that you will only receive your documents via Wifi and also Amazon send you an email with a link to download to your PC
OR
2) Use your free kindle email address which is in the format for example:
leaston@free.kindle.com - so basically you add in the free. to your regular Kindle email
You can send unprotected Microsoft Word, PDF, HTML, TXT, RTF, JPEG, GIF, PNG, BMP, PRC and MOBI files to your Kindle e-mail address.
I don't email a lot of files to my Kindle - I mostly use it when I've typed up a recipe online and I want to send it to my Kindle either as a text file or Hmtl file. I am lazy and don't plug my Kindle in via USB very often!
See more about emailing to Kindle here:
http://www.amazon.co.uk/gp/help/cust...deId=200493090