Opait Viewer - Overview

Opait Viewer is probably the World's smallest full featured application for viewing both PDFs and several other file formats. It is based, in parts, on the open source pdfium rendering engine that is actively developed by Google for use in their Chrome browser.

Opait Viewer is a 64-bit application for Windows 10 or 11 environments and consists of a single 2.5 MB signed executable that does not need any installation.

The single executable can be freely copied to local directories, placed in network locations for multi-user access or executed directly from the Internet.

Opait Viewer comes packed with features that you will normally find in much larger programs and some that you will not find anywhere else!

Free Software

Opait Viewer is free for personal or business use.

Mega PDF Viewing

Opait Viewer can easily and efficiently open multi-gigabyte PDF files with huge number of pages. The current limitations are at over 16 million pages, and up to 40 million PDF objects. These limits are unlikely to be breached and can be improved if a need arises. The Viewer automatically selects from among multiple algorithms to preserve its efficient rendering at all document sizes.

Reading Order

Opait viewer implements an advanced layout-aware text sequencing algorithm. This is a unique feature that allows automatic detection of sentences, paragraphs and text segments. Text is placed into the correct reading order allowing proper search and extraction.

After loading a document into the Opait Viewer, you may press the F12 function key to activate a debugging toolbar that shows how the text is assembled into words, line segments, text blocks, etc. Without this extra processing, text cannot be reliably extracted from some PDF documents.

The text sequencing algorithm also automatically detects a document title when one is present. This feature is particularly useful with scientific articles and reports.

OCR Text Panel

The viewer has a text panel with a list of sentences in the document. These could be regular PDF text streams or hidden text placed behind a page image by OCR engines.

As you browse the sentences, the appropriate regions on the PDF page are highlighted. This feature is particularly useful when verifying the hidden OCR text within scanned PDF pages.

Text Summarizer

A built-in text summarizer can extract important sentences and key phrases from any PDF document. This feature works well when there is a central theme to the content of the document (e.g. news or scientific articles). An extractive algorithm is used for text summarization which is language agnostic.

Input Formats

Opait Viewer can open these file formats:

Output Formats

Opait Viewer can save documents as:

Text Search

Opait Viewer allows searching for word and phrases, as well as, regular expressions. Search hits are displayed and highlighted in-context.

Interactive Features


Opait Viewer has extensive API for both composition and rendering of PDF documents. With the API, it is easy to embed the full function of the viewer into Windows applications.

The use of the API in applications requires a development license. Please Contact us for details.

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