I have several .docx files that I regularly use at work. They have various lines and boxes for information entry. When I perform the function that uses these documents, I would like to simply type the information on the lines and in the boxes instead of handwriting everything to make it look more professional, etc. When I type a date or other data on a line, it interrupts that line and shifts everything else out of line as I type. Is there a way to prevent this from happening, i.e. a way to "lock" the document format so I can just type over it, so to speak?

There are several ways to do this, the simplest being putting your entry points in a table with bottom cell borders instead of underlining and with fixed cell size. You may want to be using legacy form fields rather than content controls for this with a locked form.

See the Dian Chapman articles linked in my Forms page.

Have you tried overtype? I see from the Helps that Microsoft now protect users against accidentally doing this, but it seems you may still have a chance of doing it on purpose <g>