Size

• According to MindProd.com, a PDF file is larger than an HTML file of the same content. This makes viewing and downloading PDFs take longer than it does for other web pages.
  
  

User Compatibility

• Unlike HTML, which is commonly used to create websites and online content, PDF files require an extra program or add-on capable of reading them. While these programs are typically free, it's inconvenient to have to download a separate program to view PDFs.
  
  

Editing Difficulty

• PDF documents can be difficult to edit. Unlike word processors, you don't simply open a PDF program and start typing, a lot of formatting and technical knowledge is required to fully take advantage of this file type.