There are two reasons an applicant's resume can look weird.
#1 They didn't do a great job of formatting it, or weren't careful enough and it simply is how they sent it.
#2 When the system converted it to pdf (for easy viewing in your browser) it had trouble interpreting the formatting and the converted file doesn't look the same as the original.
Luckily, there's an easy way to access the original documents that the candidate supplied, to confirm which is the case for a specific candidate - In summary, clicking on the Docs button on the Candidate Profile will allow you to see and download the original files. For more details check out this help article.