What is Reflow in PDFs

Product

Advanced Editor (Web-based CL PDF)

CommonLook PDF Desktop Version

CommonLook Edu

Feature

Reflow

Document Element

Reflow Behavior and Limitations

Overview

Reflow is a viewing mode in Adobe Acrobat that lets someone read a document by scrolling straight down the page, instead of scrolling down and then left to right to follow columns or a layout. It's a helpful option for people using screen magnification or a smaller screen, since they don't have to hunt around the page for the next piece of content.

The order content appears in when a document is reflowed isn't determined by how the page looks. In Acrobat today, it comes from the order of content in the Content panel, which follows the currently supported PDF specification, PDF 1.7. This is a separate thing from the Tags tree, which is what screen readers use to read a document aloud. The PDF 2.0 specification actually defines reflow differently, basing it on the order of content in the Tags tree instead of the Content panel. Acrobat doesn't fully support PDF 2.0 yet, but some other PDF processors already do, so a document can reflow differently depending on which software is used to view it.

Because reflow in Acrobat depends on Content panel order rather than the Tags tree, putting a document into reflow can sometimes produce results that look strange or out of place, even in a document that's tagged correctly. That's what this article walks through.

Prerequisites 

Before reading further, it helps to know:

1. That Acrobat's Content panel and Tags tree are two different things: the Content panel reflects the order content was added to the page, while the Tags tree reflects the reading order you've set up for screen readers. See [Understanding the Tags Tree and Content Panel] for more detail.
2. That CommonLook PDF never changes the physical appearance of a document. Every change you make in CommonLook PDF affects the tag structure only, never how the page looks or prints.

Common Problems

Reflow issues usually come from two places: content that's ordered differently in the Content panel than it appears visually on the page, and content that's marked as an Artifact element. Artifact elements (things like decorative background graphics) are removed from the page entirely when a document reflows. Here are a few real examples of what this can look like.

Content Moves Out of Order

On a title page that isn't in reflow, the text "Colorado Springs" appears at the top of the page, above a photograph, followed by the text "2000 to 2024 Strategic Report."

In reflow, the same page shows the photo first, then "Colorado Springs" underneath it, overlapping the words "2000 to 2024 Strategic Report." White text reading "2020 to 2024 Strategic Plan," which wasn't visible in normal view at all, also appears.

This kind of shift happens because the Content panel order doesn't match the order content appears in visually. It also means content tagged as an Artifact element, like a footer that appeared at the bottom of this same title page in normal view, disappears entirely in reflow.

Artifacted Content Disappears

A Table of Contents in normal view shows dot leaders connecting each entry to its page number.

In reflow, the dot leaders are missing, and there's no space between the entry text and the page number. In this particular document that's just a readability issue, but if a Table of Contents entry ends in a number right before the page number, the two numbers running together could be genuinely confusing.

Tables Can Become Hard to Follow

A data table has two column headers in white text on a blue background, then a row labeled Airport with a short list in the left column and a longer, four item list in the right column, followed by similar rows for City Clerk and City Council. The table's cell borders make it easy to see where each row and cell begins and ends.

In reflow, several things happen at once: the white column header text disappears completely, the row labels move to the left and wrap across multiple lines, the cell borders vanish, and the lists inside the cells become much harder to read. Together, this makes the table's structure difficult to follow even though nothing about the tagging changed.

Steps to Follow

CommonLook PDF doesn't change the physical appearance of a document, so it isn't able to correct how Acrobat displays content in reflow. If reflow behavior is a concern for a document you're working on, you have a couple of options:

1. Let Adobe know you'd like to see fuller support for PDF 2.0 in Acrobat, since that's what would base reflow order on the Tags tree instead of the Content panel.
2. If a document needs to reflow accurately right now, recommend that the people reading it use a PDF processor that already supports reflow based on PDF 2.0 tag order, rather than Acrobat.

Frequently Asked Questions

Does CommonLook PDF fix reflow issues?

No. CommonLook PDF follows a core rule that it never changes the physical view of a document, and reflow in Acrobat is based on the Content panel rather than the Tags tree. Since CommonLook PDF only edits the tag structure, it has no effect on how content is ordered in the Content panel or how it appears in reflow.

If reflow looks wrong, does that mean my tagging is incorrect?

Not necessarily. A document can be tagged correctly, with an accurate reading order in the Tags tree, and still look disordered in reflow, because Acrobat currently reflows based on the Content panel, not the Tags tree.

Will reflow behavior change in the future?

Likely, yes. Once Acrobat more fully supports the PDF 2.0 specification, reflow will be based on the order of content in the Tags tree instead of the Content panel, which should bring reflow order much closer to the reading order screen reader users already experience.