No probs Geoff. Hope you're sitting comfortably 🙂
In Acrobat Pro go to Advanced>Document Processing>batch processing.
You should have a popup window called batch sequences.
Click the button called 'New Sequence' and give it a name when prompted
A new panel will appear – Click on 'Select Commands' and scroll down until you get to an option saying 'Security' on the left hand side. Then click 'Add'. You can include any other options from the list in the same way (such as watermark) to run at the same time as the Security settings.
Click on the grey triangle next to Security, which should have appeare d in the Right Hand Panel. A drop down called 'Security Method:None' will appear. Highlight this and then click 'edit'.
A new pane will appear with a dropwdown list. Select password security from the dropdown. This will reveal all of the security options for the PDF.
Check the box 'Restrict Editing and Printing'. Low-res printing will be okay for most purposes. You will can enter a password and so on. You also have the option to restrict changes to the pdf, so might be worth selecting 'none' for this.
When you have okayed the settings and then closed the panel behind, you will be returned to the original 'Edit Batch Sequence' screen. Under '1. select sequence of commands' you should now see 'security' has been added with your personal settings.
Under option 2. 'Run Commands on' you can select the folder with all of your pdf files in and 3. 'Select Output Location' is fairly self explanatory.
When finished this has set up a preset, so you can OK it and return to the main batch sequence menu. Select your preset and 'Run Sequence' and that should be it.
Hope that wasn't too much waffle. Drop me a line andrew_brough(at)hotmail.co.uk if there's anything.