PST file won't open—how can I recover my emails?

Back up every PST first. If one will not open, close Outlook and run SCANPST.EXE against a copy; repeat if it reports remaining errors. Then use classic Outlook to import each repaired PST: File > Open & Export > Import/Export > Import from another program or file > Outlook Data File. Select the Microsoft 365 mailbox and enable Include subfolders. This supported route retains message attachments and folder hierarchy.

For many users or large batches, ask a Microsoft 365 administrator to use Purview’s PST Import service with network upload and a mailbox mapping file. Keep the original PSTs until item counts and spot checks match. PDF is separate: Outlook can print individual messages to Microsoft Print to PDF, but Microsoft provides no bulk PST-to-PDF workflow that preserves folders and attachments. Avoid converters until your organization has reviewed their security and compliance.