Sumatra PDF is a PDF, ePub, MOBI, CHM, XPS, DjVu, CBZ, CBR reader for Windows

How to edit a document in Sumatra PDF?

How to edit a document in Sumatra PDF

Sumatra is a reader, not an editor, so we don’t have editing functionality.

[Related discussion at How to fill PDF forms offline?]

Since this seems to be the go to post with the highest hits on the topic

SumatraPDF does not have editor functions
However may modify PDF (and some other files) via additional functions, for a relatively simple solution (cpdf.exe is one extra small command line file) to permanently rotate one or more pages see Please add Tool for Rotating Pages Permanently - #4 by GitHubRulesOK

To be clear an editor changes the original data or structure and there are many tools to simply split rotate or merge pages. See

Annotations can be appended to the file without editing the primary source

So additions fall under the common term Annotation which is available in pre-release versions.

Form Filling is one type of adding text see above link: How to fill PDF forms offline?.

Highlighting Areas is another form of adding color, say to highlight some text, content comments or notes can be shown with the highlight.
Comments can also be attached as a Text Icon to perhaps place in the margin or added as a block of visible “Free Text”, if there is space.

Embedding external files or even associating external notes are other types of addition

For current examples see

See the first earlier discussions at

Signatures / DRM are IMHO a waste of life’s resources for the oil seller, author, editor, cracker and reader, they are in an addition class of their own, and frequently targeted / often broken. Added to the file to say the original was at one time sealed and is not now changed ! the first breach is the reader has to unpack it to see it ?
Topic at How to add signature into Sumatra PDF?