Action Details
Requirements and how-to articles for LinkedIn's action:

You can upload and share documents with your network.

You need this to get it done:

The document you wish to share. You can upload a file directly from your computer, or from cloud storage (Dropbox/OneDrive.)
File format: .ppt/.pptx/.doc/.docx/.pdf
Maximum file size: 100MB
Maximum length: 300 pages
Note that you can edit the description of your document or remove the post after it’s uploaded, but you can’t change or edit the document in the post. Additionally, for accessibility purposes, members who can view your post will be able to download your document as a PDF.
Document Title
Add a descriptive title to your document (maximum of 58 characters.)
Here you can go into more detail about the contents of your document/why you think it's important for people to read/etc (maximum of 1,300 characters.)
You can choose who your post is visible to - Anyone, Connections only or Group members. You can also choose whether to enable or disable comments on your post.
Hashtags (optional)
You can add hashtags to your post in order to help it get discovered by other users. However, be careful not to add too many (the optimum number is generally believed to be between 3 and 5) as it could risk looking like a spam post.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Posting and Sharing Content - Overview | LinkedIn Help
How to write a post and share it with fellow LinkedIn users.
Upload and Share Documents on LinkedIn | LinkedIn Help
Information and requirements for uploading and sharing documents.
Link missing here or found errors? Improve How-Tos