Grid lines display in PDFs exported from ArcGIS Pro

Description

When applying transparency to a raster image and exporting the layout in ArcGIS Pro to PDF, grid lines display on the image.

Cause

ArcGIS Pro natively supports transparency in any layer, and because of this display, artifacts may be encountered in a PDF reader when an output raster layer contains transparency in multiple tiles.

It is important to note that some layers become raster layers when symbology is applied, such as the heatmap renderer for points, although they are not raster layers in an ArcGIS Pro map. Even a single raster layer can become multiple tiles of a raster layer, that is, placed like mosaic tiles to form the larger image. Raster layers are output in multiple tiles to export higher resolutions without consuming excess resources.

This issue is not reproducible in ArcMap because the output pipeline in ArcMap does not support alpha transparency.

Solution or Workaround

There are three workarounds to make the grid lines invisible:

• Open the raster in ArcMap, create a map layout, add the raster to the layout, and export the layout as PDF.
• Export using one of the image format options available in ArcGIS Pro: PNG, JPEG, TIFF, GIF, EMF, etc. The issue is resolved because this action flattens the transparency.
• Uncheck the Enhance Thin Lines option in Adobe Acrobat or Adobe Acrobat Reader. This can be done by navigating to the Edit tab and selecting Preferences. On the Page Display tab, in the Rendering group, uncheck Enhance Thin Lines.
• Use the Export As Image option. This setting rasterizes the layers altogether inside the PDF, which removes the problem of transparent tiles of imagery next to each other.

Note:
For this specific problem, Adobe support was contacted and a bug is open in the Adobe Acrobat queue.