iLovePDF is an app that gives you basically all the tools you could possibly need to work with PDF documents. You can merge and divide PDF documents, compress PDF documents, convert Office documents into PDF, convert PDFs into JPGs and vice-versa, add watermarks, rotate PDFs and block password protected PDFs.
From the main menu, you can quickly access all its features by just clicking on them. Also, you can work with documents that are locally stored (inside the device's memory), as well as PDF files that are stored in Google Drive or Dropbox. It's worth noting that if you become a premium user, you can unlock additional features.
iLovePDF is an excellent app for users who regularly work with PDF documents. You just need this one app to perform dozens of different tasks