Free and opensource PDF editors and PDF readers

 The popularity of the PDF format is continuously increasing. Even if it remains difficult to use on some devices (if the displays are small or the computing power is low), the PDF format offers unique facilities, such as the fact that the elements are not repagined and are preserved wherever and however they are accessed. 

Likewise, PDF's ability to render pages as if they were printed, with text and image together (plus, in some versions, video and multimedia), makes it unmatched. At the same time, the possibility of being signed electronically and secured opens another direction of uses in which it has no competition. In addition, even if it works hard with links, it still has the ability to work with them. 

Last but not least, it allows documents to be printed correctly (if the resolution allows it), which is a big deal.

The increasing popularity of the format and its unique and unmatched capabilities have recently led to the emergence of a large number of commercial and free solutions for creating, editing and viewing PDF documents.

The main solution is still Adobe Acrobat Reader DC. PDF documents where primary developed by Adobe. Their software - Adobe Reader - is available in free and commercial variants. The free solution, Reader DC, have a lot of limits, but still can be very useful.

Other widely known freeware are: Foxit Reader, LibreOffice Draw

Major commercial solutions are: Acrobat Reader Pro, Nitro Pro, PDFelement

The diversification of operating systems has led to the emergence of dedicated solutions for each system and type of use. Most apps of this type are available for Android, but recently most also offer installs for iOS, Windows, and even browsers (as plugins)

Also, other solutions offer particular features: SumatraPDF, PDF-XChange Editor - as freeware, or Bluebeam Revu, Foxit PhantomPDF - as commercial apps

Another serie of apps and software is represented by portable and open-source solutions. Most of that does not require to be installed.

• Evince Portable - document viewer (pdf, ps, djvu, tiff, dvi)
  Evince has integrated search, continuous or side-by-side views, thumbnails, document index support, encrypted document viewing and printing support. Evince has support for pdf, postscript, djvu, tiff and dvi files as well as some support for comic book formats.
  Downloading The Portable App
• Foxit Reader Portable (Freeware) - small and fast PDF reader
  Foxit Reader is a free PDF document viewer and creator with a rich feature set. Whether you're a consumer, business, government agency, or educational organization, you need to read, create, sign, and annotate (comment on) PDF documents and fill out PDF forms. Foxit Reader is a feature rich PDF viewer which allows you to open, view, sign, and print any PDF file. Foxit Reader is the only high volume PDF reader providing a complete PDF creation solution, providing the power of PDF creation to every desktop. Foxit Reader comes equipped with comprehensive protection against security vulnerabilities, keeping your system and company safe. Note that ConnectedPDF can not be used portably due to it requiring a locally-installed service. Learn more about Foxit Reader.
• PDF Arranger Portable - Merge, split, and re-arrange PDF files
  PDF Arranger is a small python-gtk application, which helps the user to merge or split PDF documents and rotate, crop and rearrange their pages using an interactive and intuitive graphical interface. It is a front end for pikepdf. LINK ON GITHUB
• PDFTK Builder Portable - split, collate, watermark and password protect PDF documents
• PDF-XChange Editor Portable (Freeware) - PDF editor and viewer 
  
• PDF-XChange Viewer Portable (Freeware) - PDF viewer
• Sumatra PDF Portable - PDF, Comic Book, and E-book Reader
  Sumatra PDF is a slim, free, open-source PDF, DjVu and comic viewer for Windows. Sumatra has a minimalistic design. Simplicity has a higher priority than a lot of features. It's small and starts up very fast. Both the 32-bit and 64-bit versions are included for large file support, especially comics. DOWNLOAD PAGE