Text size changes in document

When starting reading a document in Digital Editions, initially the text fills a line in normal fashion, ie is fully readable. Suddenly, in a new chapter, the text goes beyond the line, ie it disappears from reading, both at the beginning as well as at the end! Is there any sizing available for the text as such. I have tried different Page View changes but that does not solve the problem.

Note: I am reading it in a Windows PC.