Quip: Team Documents for Slack - Create, share and get notified about Quip docs in Slack
Anvil PDF Filling API - The easiest way to programmatically populate any PDF
Trainual + Slack Integration - Capture knowledge or access training right inside Slack
PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
DocuExpert - AI powered document processing and review software
KDAN Mobile PDF Reader - PDF Reader is the one app you can rely on when you need a portable solution to work with PDFs.