Hello.
About displaying pcd files.
Are there any restrictions on the directory in which the PCD file is placed at that time?
If the file is placed under a static directory, it can be displayed, but not if it is placed in any other directory.
Also, can both relative and absolute paths be used to specify paths?
Web applications cannot access local directories (except exotic APIs which are not worth mentioning due to questionable cross-browser support 
) - only webservers can.
You can put the files anywhere you desire - but afterwards, you have to make sure your webserver retrieves that file from that specific path properly, and returns it to the webapp (bundlers like vite / next / CRA have different rules regarding that, express.js / webpack allow you to define all these rules yourself. You’d need to consult the documentation of the specific tool you’re using to see where you should be putting static files - most of the time it’s acceptable to put them either in src/, public/, static/ or assets/.)
as a rule of thumb, all bundlers collapse /src. that folder does not exist in production, look into /dist to see what the bundler sees, and what ends up on the server. everything inside /src is drawn out and bundled into a single file. if you url fetch from it, that path is automatically invalid, same goes for src-relative urls, invalid. you can import from /src though, including binary assets. otherwise /public is for static files, put your pcb in there. this applies to all files btw, every local asset you url-fetch is inside /public without exception.