Set new document, open and save preferences in TextEdit on Mac
You can set preferences for all new TextEdit documents, and for opening and saving documents.
Set new document preferences
In the TextEdit app
on your Mac, choose TextEdit > Preferences, then click New Document.Select a default format.
Rich text allows formatting, such as bulleted lists, that plain text doesn’t.
Select “Wrap to page” to wrap text within the document’s page margins.
Otherwise, text wraps to the document’s window size.
Set a default window size.
Choose default fonts for plain text and rich text documents.
For rich text documents you can add document properties, such as the author’s name.
Select any additional options.
You can change any document’s format at any time using the Format menu.
Revert to the default new document preferences
In the TextEdit app
on your Mac, choose TextEdit > Preferences, then click New Document.Click Restore All Defaults.
Replace text automatically
You can set TextEdit to automatically replace text in new documents. For example, if you type “teh”, it’s converted to “the”.
In the TextEdit app
on your Mac, choose TextEdit > Preferences.Click New Document, then under Options, select “Text replacement”.
You can set up the text you want to replace in the Text pane of Keyboard preferences. To open the Text pane, choose Apple menu 
> System Preferences, click Keyboard, then click Text.
Use curly quotation marks and em dashes automatically
You can set TextEdit to automatically substitute curly quotation marks for straight quotation marks and an em dash (—) for double hyphens (--) in new documents. These substitutions are called “smart quotes” and “smart dashes”.
If you need to use straight quotes and hyphens when you edit plain text or HTML documents, in plain text or code-editing mode, you can set TextEdit to use smart quotes and dashes only in rich text documents.
In the TextEdit app
on your Mac, choose TextEdit > Preferences.Click New Document, then under Options, select “Smart quotes” and “Smart dashes”.
Select “Smart quotes and dashes in rich text documents only”.
You can also set the quotation mark style using the Smart Quotes settings in the Text pane of Keyboard preferences. To open the Text pane, choose Apple menu > System Preferences, click Keyboard, then click Text.
To change the smart quote style in a document, choose Edit > Substitutions > Show Substitutions.
Set open and save preferences
In the TextEdit app
on your Mac, choose TextEdit > Preferences, then click Open and Save.View HTML code: Select “Display HTML files as HTML code instead of formatted text” to always view the HTML code when opening an HTML file.
View RTF code: Select “Display RTF files as RTF code instead of formatted text” to always view RTF directives when opening an RTF file.
Use .txt extension for plain text files: Select the tickbox under When Saving a File to use the .txt extension when saving a plain text file.
Set encoding options: Choose plain text encoding options from the Plain Text File Encoding menus.
Set HTML options: Choose HTML file settings from the HTML Saving Options menus.
To include code to preserve blank areas in HTML documents, select “Preserve white space”.