You can easily make a closed Word document read only by changing its properties. Please follow below steps to configure:

1. Open the folder containing the specified Word document, right click the Word document, and select Properties from the context menu. See screenshot:

2. In the popping out Properties dialog box, please check the Read-only option at the bottom of this dialog box, and click the OK button. See screenshot:

From now on, the Word document will be opened in Read-only view only as below screenshot shown:

If you need to make an opening Word document read only after editing, you can apply the Restrict Editing feature to get it done easily.

1. Click Review > Restrict Editing to enable the Restrict Editing pane. See screenshot:

2. In the Restrict Editing pane, please (1) check the Allow only this type of editing in the document option, (2) select Filling in forms from the below drop down list, and then (3) click the Yes, Start Enforcing Protection button. See left screenshot: 3. In the opening Start Enforcing Protection dialog box, please type password into both Enter new password (optional) and Reenter password to confirm boxes, and click the OK button. See below screenshot: 4. Close the Restrict Editing pane.

From now on, the whole document is read-only, and any users are prevented from editing this document.

Note: For turning off the Read-only view, please (1) click Review > Restrict Editing to enabling the Restrict Editing pane, (2) Click the Stop Protection button, and then (3) type the specified password in the popping out Unprotect Document dialog box. See screenshot:

Other than Restrict Editing feature, you can also make an opening Word document read only by configuring the Save As Tools in Word. Please do as follows:

1. Click File > Save As > Browse.

2. In the Save As dialog box, please click Tools > General Options. See screenshot:

3. In the coming General Options dialog box, please check the Read-only recommended option, and click the OK button. See screenshot:

4. Now you return to the Save As dialog box, please click the Save button directly without specifying destination folder and file name at all.

Notes:
(1) If your Word document has never been saved before, you need to specify the destination folder and file name in the Save As dialog box as normal.
(2) If Microsoft Word warning dialog box pops out as below screenshot shown, please click Yes button to go ahead.

5. Close the current Word document.

When you open the Word document later, a dialog box will come out and tell you this Word document is read-only as below screenshot shown: