While Stirling PDF and PdfDing are both self-hosted web applications centered around PDF files, they still differ in their use case. Stirling PDF focuses on performing various operations like splitting, cropping and rotating on your PDFs. PdfDing however has a different focus, it is all about reading and organizing your PDFs. All features are added with the goal of improving the reading experience or making the management of your PDF collection simpler. PdfDing’s editing functionalities were added with the same idea in mind. You can add annotations, highlighting and drawings to PDFs, so that you can highlight or add information that will be beneficial to your reading experience.
It talks about taht in the README :)
Let me paste it here for you :
While Stirling PDF and PdfDing are both self-hosted web applications centered around PDF files, they still differ in their use case. Stirling PDF focuses on performing various operations like splitting, cropping and rotating on your PDFs. PdfDing however has a different focus, it is all about reading and organizing your PDFs. All features are added with the goal of improving the reading experience or making the management of your PDF collection simpler. PdfDing’s editing functionalities were added with the same idea in mind. You can add annotations, highlighting and drawings to PDFs, so that you can highlight or add information that will be beneficial to your reading experience.