Create SavedSearch Criteria Using OR not AND
Yes, you can:


Select Finder. Create a Smart Folder using the key combination Option+Command+N
Click the + icon. Kind is any is the default search rule. Leave it for now. 
Most important step: Hold down the Option key. You will see the + icon change to …
Simply click the … icon to add conditional criteria. Use the default, "Any : of the following are true”
Specify the criteria using two rules: Kind is Document and Kind is PDF
Now, delete first search rule made in Step 2. Here is a screenshot of the result:




As you can see, “any of the following..” functions as “or” (versus “all of the following..” which functions as “and”)