Papermind - Papermind Slack App is a collaborative article-editing and document management platform for Slack
pdflayer - Free, powerful HTML to PDF API supporting both URL and raw HTML conversion. Unlimited document size, lightning-fast and compatible PHP, Python, Ruby, etc.
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
TeamInk - Create, search and assign documents directly from Slack
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents