Adobe Reader, while perhaps the industry standard, has nevertheless become bloated in size. Version 10.1.2 is over 53Mb, an onerous download for anyone without broadband internet. It is larded with features that the ordinary user will never need. Conversely, it lacks one critical feature: it will not allow users to save edited documents to another pdf file—that is, unless you happen to have Adobe Acrobat X Standard, Adobe Acrobat X Pro, or Adobe Acrobat X Knowledge Worker Suite. Not very likely!
The following alternative pdf readers are much smaller in size but will more than adequately serve the needs of most users:
A stripped-down, bare-bones pdf reader that occupies less than 2Mb of space. It has no tabs for multiple documents; no bookmarking feature; no comment/annotation capability; and it does not accommodate fillable form pdf files. However, if all you need to do is view a single ordinary pdf document, SumatraPDF will fill the bill nicely.
Both of these are excellent, full-featured pdf readers. Both allow tabs for loading multiple documents. Both have bookmark features, and both allow annotation via comments. And not only to they both accommodate fillable form documents, but they also both allow users to save edited documents directly to another pdf file, unlike Adobe Reader.
I lean toward Foxit Reader because its user interface is a little more pleasing to the eye and because it also has available a spell-checker for correcting any notes you might add to a document. That add-on comes with one minor annoyance: every time you download and install a new upgrade to the basic program, you also are prompted to download the spell checker add-on all over again. A small price to pay.
With or without a spell checker, both Foxit Reader and PDF-XChange Viewer are marvelous alternatives to the oversized and underperforming Adobe Reader.