PDFs exported from InDesign and viewed in Chrome display inconsistent font weights, and the issue appears to be linked in some way to ligatures.

In my own testing, I have found the following, but I am not entirely confident that this is a complete picture of the problem:

• Ligatures turned on everywhere = lighter text
• Ligatures turned off everywhere = bolder text
• Ligatures turned on in some places = inconsistent font weight line by line. Not certain if there is a regular pattern to these inconsistencies.

Issue seems to present only when exported PDFs are viewed in Chrome, but I have not tested extensively. Issue seems to persist regardless of any PDF export settings.

Tested most thoroughly with Roboto font, but upon quick checks the issue appears to occur with others, too.

Issue is most noticeable with white text on a colored background, however it is more subtly noticeable with a white background, as well. Issue occurs in documents with no transparencies, so that does not appear to be a root cause (I mention as the only other reported examples I could find of inconsistent font weight in PDF exports were apparently related to having transparent objects such as shadows and PNG images in the document).

I believe I have found examples of this issue in InDesign-generated PDFs found on the web, as well (e.g. attached GoToWebinar PDF, pp. 2–3: note how lines including the ti ligature are lighter than others). As a result, I don't think the issue is specific to my machine/installation.