if attached project in \bin\debug\long you will find original.pdf and original_new.pdf where text replacement is done. Unfortunately, when text is replaced with longer text (just run project) new text goes out of page.
We were able to reproduce the issue in our environment. Therefore, it has been logged as PDFNET-52233 in our issue tracking system. We will further look into its details and keep you posted with the status of its correction. Please be patient and spare us some time.