Outlook handles PDFs the same way Gmail does — preview only. For editing, you download. The flow is straightforward; the trick is doing it in the browser without bouncing through Word or Acrobat.
From Outlook web
Open the email. Click the PDF attachment. Click the download icon (or three-dot menu → Download). File lands in Downloads.
Open Flint in another tab. Drag in the downloaded file. Edit, sign, or compress as needed. Download. Reply to the email and attach the edited version.
From Outlook desktop
Same idea: right-click the attachment, Save As, pick a folder. Open Flint in your browser. Drag the saved file in. Edit. Save back. Attach to reply.
Outlook desktop has 'Edit in Word' for PDFs — same trap as OneDrive (converts to Word, breaks layout). Skip it for PDF-format-preserving edits.
OneDrive integration
Corporate Outlook often integrates with OneDrive. Save attachments to OneDrive, edit a copy in Flint, upload edited version back to OneDrive, attach as cloud link in your reply. Cleaner for long document threads.
FAQ
Can I use Office Lens or other Microsoft tools?
Office Lens scans paper to PDF — different job. For editing existing PDFs from Outlook, you need a PDF editor. Flint covers it free.
Will recipients know I edited the file?
Standard PDF files don't carry edit indicators. Recipients see the file you attached; they don't see your changes vs. the original unless they compare manually. Mention edits in the email body for clarity.
What's the attachment size limit?
Outlook.com is 20 MB; corporate Exchange varies (usually 35 MB). Beyond that, Outlook offers to upload to OneDrive and send a link. Compress in Flint to avoid hitting the limit.
Outlook attachment → Flint edit → reply with the polished version.