how to use the same Google Search operators more than one at one

Question

Such as ,I want to use filetype operators to search ".doc" and ".pdf" file at once on Gooogle.
However, one filetype operator can only support one argument.
I looked in  advanced search  of Google,but I found it can not be implemented.

Ravinder C · Accepted Answer

Hi DwightSir,
Welcome to the Google Search Help Community!!
You can use symbols or words in your search to make your search results more precise.
 Google Search operators depend on search techniques
Search social media
Put @ in front of a word to search social media. For example: @twitter.
Search for a price
Put $ in front of a number. For example: camera $400.
Search hashtags
Put # in front of a word. For example: #throwbackthursday

Exclude words from your search
Put - in front of a word you want to leave out. For example, jaguar speed -car

Search for an exact match
Put a word or phrase inside quotes. For example, "tallest building".
Search within a range of numbers
Put .. between two numbers. For example, camera $50..$100.
Combine searches
Put "OR" between each search query. For example, marathon OR race.
Search for a specific site
Put "site:" in front of a site or domain. For example, site:youtube.com or site:.gov.
Search for related sites
Put "related:" in front of a web address you already know. For example, related:time.com.
See Google’s cached version of a site
Put "cache:" in front of the site address.
For more information article for help: 
Refine web searches
Regards
Ravinder Chauhan