Papal Documents Online has many older documents already converted to epub and mobi format. Just go there and follow the links. However many documents link directly to Vatican editions with their yellow parchment background. If you run into one of these you must go through an additional step to get it into your reader. First download a copy of Calibre, an excellent ebook management tool. Go to the document you desire and save it in txt format by right clicking it in your browser. Next open Calibre and input the document into the library. I did it by just dragging it from my desktop onto the library screen. Select the document in the Calibre library screen and click on convert in the menu bar. The last step is to save your new document and copy it to your reader.
Remember, under Canadian law, copyright protection extends for the life of the author plus fifty years which means that any document up to Pope Pius XII may be copied and circulated freely. However, it is illegal to distribute copies of Evangelium Vitae without approval from the appropriate ecclesiastical authorities. For that matter, it would probably be illegal for me to meet Barona in a back alley somewhere and slip him a bootleg copy of Evangelium Vitae... sorry about that.