Sometimes when a Windows user exports their text messages with Decipher TextMessage, the exported HTML file will automatically open in Notepad and not with the user's web browser. The exported file needs to be opened in a web browser (Chrome, or Firefox, or Internet Explorer 9 or higher) in order to view the exported messages with chat bubble formatting.
To ensure that this happens, simply right-click on the exported HTML file and then choose "Open with" and select one of the aforementioned web browsers. The exported HTML file will then open and all your exported messages will be displayed in chat bubble format as intended. From there you can also make a PDF of the messages if you desire to to so.