How do I create a link on the iPad home screen to a specific pdf?
First simple way, it requires Google Drive, however.


Open the iOS Google Drive app, upload your desired PDF and get the link of said PDF.  
Open iOS Safari and open the link in the browser; you should now see the PDF in Safari.
Click "Share" and then "Add to Home Screen". 


Second complicated way, but goes to iBook; you will need Workflow the app.


Get Workflow the app; open it, create a new workflow (click plus sign)
Find the "action" Get File and drag it to the right "building area".   
In the Get File action, uncheck "Show Document Picker"; you will see two new formlists pop up.
In the "iCloud File" form, type in any name, for now lets go with name.pdf; it should now look like: 



  iCloud File  /Workflow/name.pdf



Search the actions again for the action "Open in iBooks" and drag it over as well.
Swith to laptop (easier) and you must get the desired PDF, rename it to name.pdf, copy/move it to your iCloud Drive and into the Workflow folder. 
(if it doesn't exist, make a Workflow iCloud Account via the app)
Go back to the app, test the workflow we built by pressing the play button and it should open the PDF in iBook! 
Lastly, press the gear and then press "Add to Homescreen", and ta-da! You now created a button on your homescreen to open your pdf in iBook!