Begin your text with a first line exactly like this:
.LOG
Then save the document. Every time you open a file which begins with this line, tpad will automatically insert the locale specific current date and time to the end of the text (this is the same as manually choosing Date/Time from the Edit menu).
You can also use this function to write your diary with tpad!
By default this facility is turned on. If you don't want it, just set the variabile logfac to no in tpad configuration file.
The only effect of tpad(logfac) being yes when tpad is used in readonly mode (i.e. as a pager) is to automatically scroll till the end of the text whenever a log file is opened. No new date and time will be inserted in this case.
To avoid scrolling to the end of the text when you open a log file you can use the goto line command option. For example:
$ tpad +1 mylog.log $ tview +1 diary
Last modified: Sunday, 18-Apr-2010 09:37:30 UTC