Okular — The Complete Guide: Viewing, Annotating and Verifying Digital Signatures in PDFs
Okular is an open-source document viewer from KDE. Beyond reading PDF, EPUB, DjVu, Markdown and images, it offers two things engineers need: annotating drawings and reports, and checking digital signatures.
Okular
KDE
KDE’s document viewer — read and annotate PDFs with highlights and notes, and verify digital signatures.
Get it from the vendorWhat you get
- Annotation mode — notes, highlights, underlines and free text.
- Signature verification — is the signature valid, and was the file changed after signing.
- Signing documents — apply a digital signature from the viewer.
- Many formats — PDF, EPUB, DjVu, Markdown and images.
- Open licence — GPL-2.0, free including commercial work.
Who it suits
Anyone who receives contracts, approvals or signed drawings and wants to confirm they have not been altered. Okular runs on Linux and Windows (installing from the Microsoft Store is recommended); for macOS only experimental nightly builds exist.
Related tools
For fast viewing on Windows — SumatraPDF. For editing and comparing versions — PDF4QT. For handwriting on a PDF — Xournal++.
SumatraPDF
Krzysztof Kowalczyk
A tiny, very fast PDF reader for Windows — opens heavy drawings instantly, and reads ePub and DjVu too.
Get it from the vendorPDF4QT
Jakub Melka
An open PDF editor and viewer — annotations, page organising, signing, redaction, plus a tool to compare document versions.
Get it from the vendor
Xournal++
Xournal++ team
Handwriting and PDF annotation with a stylus — markups on drawings, lecture notes and problem solving.
Get it from the vendordiff-pdf
Vaclav Slavik
Visual comparison of two PDF versions — see at once what changed between revisions of a drawing or report.
Get it from the vendorThe bottom line
One viewer that both marks up documents and checks signatures — a serious, free alternative to a commercial PDF reader.