Im want to make post editor for Page Content (for good typography, like set up right dashes and quotes), i may call it every time i render page, but better and quicker solution is change Content before saving. So how i may do it?
Thank you.

You can define a onBeforeWrite function on your page type. Eg if you want to edit the page content before you write to the database you would need to add this to your mysite/code/Page.php in the Page class

function onBeforeWrite() {
// do something
parent::onBeforeWrite();
}

For more information see http://doc.silverstripe.com/doku.php?id=datamodel#onbeforewrite