The Library subscribes to hundreds of databases, and many of these allow you to download results in PDF form to read later.
Look for the option to Download PDF or email the article to yourself.
PDF files are sometimes easier to read when extra white space in margins are cropped. Tools for cropping include: PDFScissors, Briss, OSX Preview, GoodReader for iOS, Adobe Acrobat
If you have one or more of these installed, when you select Open In... you will be given a choice where to open and save your file.
PDF reading and management in Android, all free:
Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share your research sources.