Here are some free options for editing PDFs if it's YOUR doc. If it's not your document you will need a couple of things: 1 - permission to edit before publishing, and 2 - a way to edit the pdf (app, software, etc.)

I used DocHub (which is a free Chrome app) to remove my chapter of Behind Her Brand: Direct Sales Edition, a book I co-authored, in order to create a PDF giveaway in one of my apps, but I made sure I had permission from the publisher to do that first.

Another easy free option is PDF Escape.  And PDF Buddy is popular too.

If you prefer using a mobile app, check out PDF Expert - Edit, annotate and sign PDF documents by Readdle.

There are a lot to choose from!

My favorite apps for scanning doc by taking a picture with my phone and creating a pdf I can email out are...

Genius Scan - PDF Scanner by The Grizzly Labs
Tiny Scanner - PDF scanner to scan document, receipt & fax by Appxy

Apps I use for signing documents using my iPhone:

DocuSign - Upload & Sign Docs
SignNow - Sign and Fill PDF & Word Documents
SignEasy - Sign and Fill PDF and other Documents - Glykka LLC
HelloSign - Scan or Import Documents to Sign