Hi Wouter,
Based on the details you have provided we understand that your requirement is to select multiple annotations and align the selected annotations. Regarding multi selection at present we do not have support for multi selection of annotations in the WPF PDF Viewer. We have already logged a feature to select multiple annotations and we do not have any immediate plans to implement this feature. At the planning stage for every release cycle, we review all open features ad identify features for implementation based on specific parameters including product vision, technological feasibility, and customer interest.
Please find the following feedback link to track the implementation of this feature.
Regarding alignment for annotations as per your mention, we have checked the requirement in adobe, in which we can select and align objects using Align options as in the below screen shot.
Kindly check the above image and confirm us whether your requirement is also the same as in the adobe align support. If our understanding is different, please provide more details about your requirement. This information will be helpful for us to analyze more on this and provide you a better solution.
Regards,
Divya