At a Glance
Adobe's popular PDF format makes files look great and Adobe's free Reader lets everyone look at the files for free. However, you can't make annotations to those documents unless someone with the full Acrobat program has saved the PDF in an editable form. If you've got a locked-down PDF, you're out of luck... unless you've got Tracker Software's free PDF-Xchange Viewer.
In addition to letting you mark up existing PDFs, PDF Xchange creates PDFs from text, RTF, image files, and scanned materials--something that you just can't do with Adobe Reader. This process is quick and easy, just select File, New Document and select your source file.
PDF-Xchange lets you add sticky notes; cross out, underline, and highlight text; add arrows, boxes, and other shapes; and add freeform drawings and markup. Just as in Adobe Acrobat, you can right-click any markup element and add a pop-up note. PDF-Xchange does not let you select text and replace it with new wording, as you can in Adobe Acrobat--and it doesn't recognize that markup from Acrobat, either. You see the text as crossed out, but the revised text is lost. This is unfortunate, since all other markups and comments appear to be compatible between programs. You can save your annotated document as a new PDF, or export it in several different image formats, including BMP and TIFF--but you can't save it as a text file.
In addition to PDF-Xchange, Tracker Software sells Standard and Pro versions that add features such as printing PDFs from Office documents and advanced PDF creation tools; at $44 and $74 respectively, they're worth considering. Before you take the leap, however, I suggest giving the free PDF-Xchange a thorough test to ensure it meets your needs. The fact that it doesn't appear to be completely compatible with Adobe Reader and Acrobat bothers me--like Adobe or not, it is the 800-pound gorilla. In addition, I do need to export text documents from PDFs from time to time, and that just isn't possible with PDF-Xchange. My reservations aside, this is a good PDF viewer and creator that will likely meet most home users' needs.