Pdf to image conversion: quality degradation and significantly increased file size

GemBox.Pdf
1

Hello, dear GemBox support team,

We use GemBox.Pdf’s PDF → Image conversion functionality to generate thumbnails.

After a fairly recent update, we noticed a degradation in image quality for text-heavy documents (it appears that original fonts and/or their weights are no longer preserved), as well as a significant increase in the resulting image file size (two times or more).

In production, we typically extract relatively small thumbnails (up to 320×320 px). However, for demonstration purposes, I generated larger images to make the issue more visible.

The GemBox versions used are:

  • “Old” version: 2025.10.106
  • “New” version: 2026.1.107

Result from the “old” version:

image
image595×841 51.5 KB

Result from the “new” version:

image
image595×841 51.2 KB

For reference, here is how the original PDF document looks (I can share the PDF file itself if needed):

image
image1002×390 47.6 KB

The difference in image file size is also quite noticeable: approximately 55 KB in the old version versus 130 KB in the new one.

Could you please advise what might have caused this change (both in visual appearance and file size), and what options are available to restore the previous behavior?

Thank you in advance.

2

Hi Yaroslav,

Please send us your PDF file so we can investigate it. You can send it via email or support ticket (see the Contact page).

Regards,
Mario

3

Hi,

Please try again with this NuGet package:

Install-Package GemBox.Pdf -Version 2026.1.111

Note that this is a hidden (unlisted) version. To install it, you’ll need to run the above command on the NuGet Package Manager Console (Tools → NuGet Package Manager → Package Manager Console).

Does this solve your issue?

Regards,
Mario

4

Hi Mario.
Thanks a lot, the issue seems to be resolved with the latest versions of the GemBox components.

5

Hi Mario,

After upgrading GemBox.Pdf to version 2026.2.105, we started experiencing two issues related to PDF thumbnail extraction. The same functionality worked correctly with version 2026.1.107.

Issue 1

  • Error message: "Invalid character was detected while reading a dictionary."

  • Method: GemBox.Pdf.PdfDocument.Save

Issue 2

  • Error message: "End-of-file was reached before literal string was read entirely."

  • Method: GemBox.Pdf.PdfDocument.Save

Unfortunately, we are unable to share the affected PDF files because they contain secured content.

Please let me know if you need any additional details.

6

Hi Ivan,

Can you please try using the code from the following post in order to remove the confidential data from the input PDF files:

If this works and you’re still able to reproduce those issue, please send us those PDF files so we can investigate them.

If this doesn’t work for you, note that you can contact us to sign an NDA.

Regards,
Mario

7

Thank you.
I’ve sent samples via email with “Thumbnail from Pdf issue” topic.