Top Alternatives to Skim

Foxit Reader is a lightweight, fast PDF Reader.

Sumatra PDF is PDF reader and writer for Windows.

Evince is a document viewer for PDF, PostScript, DjVu, TIFF, XPS and DVI formats.

PDF-XChange Viewer is a free PDF editor/reader.

Nitro Software, Inc. develops commercial software used to create, edit, sign, and secure Portable Document Format (PDF) files and digital documents.

Preview is the image viewer and PDF viewer of the macOS operating system.

CutePDF Writer installs itself as a "printer subsystem". This enables virtually any Windows applications to convert to professional quality PDF documents.

MuPDF is a free and open-source software framework written in C that implements a PDF, XPS, and EPUB parsing and rendering engine. It is used primarily to render pages into bitmaps, but also provides support for other operations such as searching and listing the table of contents and hyperlinks.

PDF Studio is a multi-platform PDF editor.

Xournal is an application for notetaking, sketching, keeping a journal using a stylus.

Nitro Pro gives you the tools to do more with your documents.

PDF-XChange Editor a small, fast, feature-rich FREE PDF editor/viewer.

qpdfview is a tabbed document viewer.

Master PDF Editor is а complete application for editing PDF documents and PDF files for Mac OS X, Windows and Linux.

zathura is a PDF viewer.

Xodo is a PDF reader and annotator.

Universal Viewer is an advanced file viewer for wide range of formats.

ezPDF Reader is the best selling, best rated and most commented multimedia and frame-animation PDF viewer, annotator, form filler and paperless solution.

Document Viewer is a highly customizable document viewer for Android.