See the section Using other Mailbox files With Kmail.
Open up the Settings window from the file menu. Click on the Network tab. Select your account from the account list and click the Modify button. This dialog contains the "Delete mail from server" setting which you must not select.
The text footer is called a signature file. What you need to do is open up a text editor (like kedit) and type in what you want to appear in the footer. Save the file under a name like signature or footer. Go into Kmail and select File | Settings... Look in the "Identity" tab for the "signature file" field. Click on the ellipses button and select the file you just created. Now Kmail will automatically insert that file in any message you write.
The word wrap setting is probably turned off. Word wrap can be toggled on and off in the Composer tab of the Settings dialog box.