Why Google can't open it
A .pub file is Microsoft Publisher's own format, and Google never added support for it. Drive will store the file and show its name, but there's no preview and no "Open with" option for Docs or Slides. On a Chromebook that leaves you with no way in at all.
First, decide what you need from the file
- Just the words, to reuse in a new document: go through PDF into Google Docs.
- The design, to edit and print again: go through PowerPoint into Google Slides.
Route 1: PDF into Google Docs (text only)
- Make a PDF of the .pub file. If you still have Publisher, use File > Export > Create PDF. If you don't, my converter makes one for $4.99, after a free preview of every page.
- Upload the PDF to Google Drive.
- Right-click it and choose Open with > Google Docs.
Google Docs turns the PDF into an editable document. You get the text, but columns, text boxes and placed pictures mostly don't survive, because Docs lays everything out as one stream of text. That's fine for a letter or a list. It isn't for a flyer, a newsletter or a bulletin.
Route 2: PowerPoint into Google Slides (keeps the layout)
Google Slides works the way Publisher did: boxes placed on a page. It can't open .pub files, but it opens PowerPoint files.
- Drop the .pub file on my converter and check the free preview of every page.
- For $12, download the .pptx: one slide per page, with every text box and picture editable.
- Upload it to Google Drive, right-click it and choose Open with > Google Slides.
Two things to check afterwards: Google Slides only offers Google Fonts, so text in other fonts is swapped and can reflow; and File > Page setup should match your paper size. To print, use File > Download > PDF and print that.
If you still have Publisher
Save a PDF of every file you'll need while you still have access (File > Export > Create PDF). The PDFs upload to Drive and open in Docs as above, and they're a safe archive either way.