Odd size letters and fonts

The problem is related to the fonts used in the PDFs you want to display. They may be damaged or not embedded correctly into the PDF, so your Reader tries to replace them with a suitable font from your local system. It's also possible that those PDFs have been created with such a poor PDF tool, that those internal structure is totally rubbish and does not fit PDF standards. Reader can manage some flaws to make the PDF still viewable but it won't fix the PDF. In those cases you can only ask the author of the PDF to create a new PDF.

Im using Windows 10 and Adobe Reader  DC latest Version. Another Example from a different PDF