Well, the question might be pretty basic, but as many others I've noticed that it is possible to merge secured pdfs either by using another program or another tool. My question is: Is it ok to merge secured pdf's or is it the intention that a secured pdf should not be merge-able as it is not editable?
Acrobat will merge secured PDFs into a portfolio; it will not do it otherwise.
The standard definines the security method and some degree of expectation. Since merging two secured documents into one must inherently remove the security from at least one, that doesn't sound a responsible thing to do.
It may seem a simple programming exercise in changing encryption to (say) the first file, but that basically offers an "easy off" option for security, since if one of the files has dominant security, then the user can easily use a document with known security to take over unknown security. Many apps do not respect security, but then many programmers do not buy into the ideas expressed in the standard.