The phrase refers to a digital document, typically in Portable Document Format, containing the text of a novel in the A Song of Ice and Fire series by George R.R. Martin. Such files offer a way to access and read the story electronically. An example would be a complete, unabridged digital version of A Game of Thrones available for download.
Accessing the text in this manner can provide convenience and portability. Individuals can read the story on various devices, such as e-readers, tablets, or computers. The availability of these digital versions can impact readership and distribution of the work. Historically, the proliferation of such digital copies has raised copyright concerns and discussions around digital rights management.