When you install Ubuntu on your computer, it comes with a standard open-source office software package. In older versions of Ubuntu, it was OpenOffice.org; in newer versions as of the time of publication, it is LibreOffice. LibreOffice has built-in capabilities that allow you to import PDF files into an editable environment and save them as .doc as well as other file formats.
Launch LibreOffice. LibreOffice is the icon on the dock that looks like a paper with blue writing on it, and it is installed on the dock by default in the Unity interface. If you are using the classic Ubuntu interface, click on the "Applications" menu, hover over the "Office" submenu and click on the "LibreOffice Documents" application.
Click on the "File" menu, then click on the "Open" option or press "Control" on your keyboard and hold it until you press the "O" key. Navigate through the folders on your computer until you find the PDF file you want to convert to a DOC file. Double click on the PDF file to open it.
Allow LibreOffice to convert the file into an editable format.
Click "File" and "Save as." The window indicating the default folder for saving files comes up. Make any adjustments to the folder you want to save the file in and choose the .doc file type from the drop-down menu. Press the "Save" button.
If you are running an older version of Ubuntu with OpenOffice.org installed as the default, download the Oracle PDF extension that allows you to import PDF files in the same manner as LibreOffice. Click on the "Tools" menu and open the "Extension Manager" to download Oracle's PDF extension. You can also download it directly from Oracle's website (see Resources).