: PagePlus X5 and above
Yes. The PagePlus dictionary feature is actually made up of several dictionaries. There is an in-built dictionary containing common words plus a separate default user spelling dictionary that you'll be able to add your own words to. For example, there may be some words you are using in your publication which are specific to your use, i.e. product names and terminology. PagePlus not only identifies such "unknown" words on the page with as red wavy underline, but during a spell check, the words can be optionally added to that default user dictionary as you check. Once you've added the words to the dictionary they will no longer appear be treated as "mistakes" and will no longer be picked up by spell checking.
PagePlus X6 also lets you create your own custom dictionaries dedicated to specific uses, e.g. medical, technical, etc.
To find out how (PagePlus X6):
Note: For PagePlus X6, you can access (and add to) the default user spelling dictionary via Tools>Options (Text>User Dictionaries)
For PagePlus X5, use Tools>Options (Text>Proofreading) instead.