Actually this is good advice. Nowadays nobody reads your CV in the first step. Your CV first gets through an automated system (ATS i think its called). It's designed to filter out as much as possible.
The problem with PDF is that it's terrible to parse cuz it's designed for humans reading it, not machines. The only reliable way to parse it is by converting it to images and then OCR, which is kinda expensive.
So before you send a PDF, you should first try to convert it to txt and see if the content make enough sense. Or just use word to make a CV then export to PDF.
When i was looking for a job, i remember there was a website that would give you tips on your CV and they had an ATS report of your CV. I was so shocked to realize that ATS totally messed up completely to parse the correct info from my latex CV. Like I have a lot of AI/ML experience and it completely missed it and thought i had quality assurance one. And i was applying for AI jobs, no wonder I couldn't get any interviews. Then I changed it to word and an exported pdf where word wasn't accepted. I got many more interviews after that.