Languages and Cultures. The biggest change in PAF 5 is that you can type and store characters from many of the world's languages. Not only can you record information in your own language, but you can type characters from the languages of any of your ancestors. Technically, the database has been redesigned to accommodate all Unicode data.
Other changes to the database include the following:
You can type optional romanized and phonetic names for individuals whose names are natively written in a non-roman alphabet (such as Hebrew, Cyrillic, or Chinese). The alphabetic index of individuals is part of the database file and not a separate file. Because of other improvements in the database format, most databases will be smaller in PAF 5 than they were in PAF 4.
PAF 5 also supports U.S. and metric measurements and international number formats through the Windows regional settings.
Single name field. PAF 5 uses a single name field for typing names rather than providing separate fields for given names, surname, and suffix titles. Surnames are marked by placing slashes around the surname. Preference options are available to help you automatically mark surnames in many cases and to prompt you to verify the automatic placement of the slashes. This change was made to make it easier to type the name in the order it was spoken during the person's lifetime. It also accommodates cultures in which family names are at the beginning rather than at the end or cultures that use no surnames or that use multiple surnames.
Unique record serial numbers. PAF now assigns each record in your .paf file a unique serial number (referred to as a UID). Like a record identification number (RIN), a unique record serial number identifies each individual in a .paf file. Unlike a RIN, a unique record serial number is unique worldwide. This means that each individual in each of your .paf files has a number different from all other individuals in all other .paf files that are made worldwide.
Those are just some of the differences, Jennifer, but take a visit to the site above for the full list (I have only copied an "edited" version here to give you some idea of what to expect).
By all means get back to me (use my address to write personally - just click on my name to bring up my address) if you need any further help with merging your two files.