I have quite a few imported files that show this kind, and I shows as lower case pdf. Importing it to another computer the same file shows as PDF+Text. So these files are basically identified wrong and I waste time trying to convert to PDF+Text. Can I change the type and remove this kind?
Not manually, no. You can drag and drop them out of the database and back in to see if that resolves it. What edition of DEVONthink are you running?