Please, see the following live demos which demonstrates how to save the RadEditor's content in a Database and in External HTML file:
Save In Database
Save in External File
Datagrid Edit Template
On the other hand, your problem is more likely related to overriding the editor content yourself, in your Page_Load method. Please note that if you read the content of the editor in an event handler (such as a button event handler) this event handler executes later in the page lifecycle compared to Page_Load. This is why, in case you set the initial content in Page_Load it is mandatory to add a check, e.g.
radEditor1.Html = "Some content";
In case you are having any difficulty, our suggestion is to implement your scenario using a simple <asp:TextBox> instead of RadEditor. Once you get the textbox to work as needed, all you need to do is change the textbox to RadEditor - and all should be fine.
In case you are able to implement your scenario with a simple <asp:TextBox>, yet you are facing trouble with the RadEditor, please send us your working project in a support ticket and we will make the change for you.
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