Could the slow down be a network issue? I have experienced this with a similar PDM/PLM. Do you have an in house IT guy to talk with?
As far as what goes into the background, I imagine the PDM software is checking the file for permissions.
You probably need to perform a Extended SQL trace profiler to understand the performance issue.
I suggest you contact your SOLIDWORKS reseller to assist you for further investigation.
Update, having trying to debug this for a bit now today. All File, Open's are on the same assembly, no state or version changes, all not checked out, read-only. Assembly has 194 components, so it's a moderate size assembly but not overly complex by any stretch.
Open time for On-Line - 1:33 (min:sec)
Open time for Off-Line - 0:11
VAR suggested looking at what was in my folder locations for System Options/File Locations/Referenced Documents. This was blank, since I recall years ago debugging something and seeing lag with folders listed here. On a whim, I added the root vault folder.
Open time for On-Line with c:\epdm added to Ref Doc - 3:21 Ouch!
Then, I recalled a few years ago we had a major lag issue with Toolbox files, which are shared within EPDM. The add-in for PDM was causing major lag when inserting Toolbox items, and when the add-in was turned off Toolbox was snappy. So I disabled the PDM add-in.
Open time for On-Line, PDM add-in turned off - 0:12 NICE!
So it appears the add-in has some sort of bug in it, again. Currently running 2017SP4 on a Win10 machine and am in the process of getting ready to roll out 2018SP1 to my 90+ users. (I'm our CAD admin) I'm going to evaluate this issue on 2018. If it persist, I'll roll the software out with the PDM add-in disabled by default, that's a huge time penalty hit.
I'm posting these details here so other users frustrated by slow PDM performance may be able to possibly benefit.
I noticed a bunch of functions that you wouldn't expect slowed down when we moved our archive server closer to us and further from the Domain Controller. We used the recommendation from S-068787 to do the following on the Archive Server and it help tremendously
• Instead of adding the domain groups directly, create a local Windows group on the archive server and add the domain users or groups to that local group instead. Add that local group to the Windows login settings (S-058096).
Also a much better tool for evaluating local client performance issues is Process Monitor:
Use it to capture everything SolidWorks.exe, explorer.exe and edmserver.exe are doing while you open the file and look for large gaps between operations and see the last thing run before that gap to get a view into what's tripping you up.