Merge enables you to edit files by typing text directly into them. Click within one of the files to make it active and then use the keyboard to make any required changes.
Use Copy 
button (Ctrl+C) to copy text from one file to the clipboard and Paste 
(Ctrl+V) to paste it into the other file.
You can also select blocks of text and drag/drop them to and from any file panel in Merge and to many other applications. Hold down the Ctrl key when you drop the selected text to copy it to the drop location, or hold down Shift to move it.
As you make changes to the files, Merge performs background comparisons to ensure that the displayed comparison results are always up-to-date.
Modified indicator
When a file has been modified, an indicator icon Modified 
appears next to the edit field at the top of the window.
Edit markers and bookmarks
As you edit files, Merge will automatically create edit markers 
to indicate lines that you have modified. Use the Ctrl+7 and Ctrl+8 keyboard shortcuts, or the Next edit 
and Previous edit 
buttons in the ribbon.
As you are comparing or editing files, you may want to set bookmarks to enable you to return to locations of interest later on. Press Ctrl+F2, or click Toggle bookmark 
in the ribbon, to toggle a bookmark on or off on the current line. To navigate between bookmarks, press F2 or Shift+F2, or use the Next bookmark 
and Previous bookmark 
buttons in the ribbon.
Comments can be added to bookmarks, making it easy to note important information or to record a question. To edit a bookmark’s comment, right-click the bookmark and choose the Edit comment menu item. Bookmark comments are shown as tooltips when you hover the mouse pointer over a bookmark.
Bookmarks and comments are included when you create an HTML comparison report or save a comparison for archival or team collaboration. They are therefore a useful tool for asking questions or making notes in a comparison that will later be emailed to other team members for review.
Undoing changes
Use the Undo 
and Redo 
buttons in the ribbon to undo or redo changes you have made while editing.
Read-only files
When a file is read-only on disk, an indicator icon Read-only 
appears next to the entry field at the top of the window.
By default, Merge does not allow you to make changes to files that are marked read-only on disk. You can turn off this protection by changing the appropriate setting on the Editing options page.
Merging files
In addition to the editing features described above, several tools are provided to make it easier to merge changes from one file into another. Please see the Merging Files topic for more information.