I realize that "how secure?" is a vague question.
The data that I carry about on my laptop is a regularly synchronized PDM standard vault in offline mode. I have a local cached copy of all my vault data because I can't usually predict what I need to access. We are not able to access the vault remotely - its PDM standard not professional.
Because the vault is in offline mode there is no need for the PDM login details to access them.
The files are stored in their normal solidworks format. You can copy them easily.
This means that unless you set to clear local cache in the PDM settings all the recent files people are using on their workstations are just stored there on the hard disc in a form anyone can find and open/copy/edit if they gain access to the workstation or the disc on the workstation.
This would apply to PDM standard and PDM priofessional. The only advantage in PDM professional would be that you can operate in online mode at a remote site, check your files in and clear that local cache so you are not carrying that data with you at all (but you don't have it unless you find internet access, and you might be waiting a while if it is slow).
Solidworks do not offer a means to add a layer of security to the access to these files as far as my VAR knows.
Things I could try:
Copy the vault data as windows file system onto a usb disc and apply an off the shelf security package to that. I'm not sure the file assembly links are going to work doing that as I think they are handled by the database? I guess I can try a sample of data...
Then clear the local cache on my laptop before travelling.
Try to apply a 3rd party security system to the local cache location that requires a login. I'm guessing that is almost certain to defeat the PDM system when logged in and at the very least cripple performance.
I raised an enhancement request. 1-16937558706 (can't seem to link to that as yet).