Google Docs can't add a password to a PDF on its own. Download the Doc with File > Download > PDF document (.pdf), then encrypt it offline in macOS Preview (File > Export > Permissions) or Adobe Acrobat, or use an add-on such as Docs to PDF Pro to export a password-protected PDF directly.
To export a Google Doc as a PDF, open it and click File > Download > PDF document (.pdf). If the Doc has tabs, choose Current Tab or All Tabs and click Export. To set margins or a page range first, use File > Print and save as PDF. On Android, tap ⋮ > Share and export > Save as.
Google Docs can't export several separate Docs as one PDF on its own. Either paste each Doc into its own tab and use File > Download > PDF document (.pdf) > All Tabs, download each Doc as a PDF and join them with a free PDF merger, or merge them with the Merge Docs Pro add-on and save one PDF.
