Microsoft 365 has 'Save as PDF' baked into Word, Excel and PowerPoint. It works well — for creating a PDF from a Word doc you authored.
Flint covers the rest. Here is the honest comparison.
Where Microsoft 365 wins
Free with any 365 subscription. Excellent for creating PDFs from documents you authored in Word, Excel or PowerPoint. Preserves your formatting because you authored the source.
Where Flint wins
Editing PDFs you did not author. Edit-pdf on an existing PDF, convert-pdf-to-word when you do not have the source, merge-pdf across PDFs, sign-pdf for contracts. 365 cannot edit a third-party PDF directly.
Best for…
365 for creating PDFs from documents you own. Flint for editing PDFs from elsewhere. Use both — they do not overlap.
Workflow tip
Author in Word, export to PDF via 365. Edit incoming PDFs in Flint. Convert PDFs to Word in Flint when you need to bring them back into the 365 stack.
FAQ
Can Word edit a PDF directly?
Word can open a PDF as an editable Word file with formatting loss. For preserving the PDF, use Flint's editor.
Does 365 sign PDFs?
Not natively. Use Flint or a signing service.
Is 365 enough on its own?
Only if you never touch PDFs from outside your own authoring.
365 makes PDFs; Flint edits them. Two halves of the same job.