"Secured" .pdf that does not open from Acrobat.com

I create documents, and spreadsheets, with OpenOffice version 4.11 as .odt files. I, frequently, then, "export" the files as .pdf files and, if I am intending to send them as attachments via email I export them as "Secure" .pdf files. When opened the filename on the top bar is shown as having "(Secured)" suffixed to the file extension, e.g. .pdf (SECURED). When I upload them to Acrobat.com they appear to upload with no problem(s). However, when I hover the cursor over the filename.ext in Acrobat.com a pop-up appears announcing that the FileType cannot be previewed and that the file must be downloaded for viewing. That is OK considering that I did save the file with a password, but that password requirement does not prevent the .pdf from being viewed. The password is only effective insofar as preventing any amendments/edits being applied to the content of the .pdf and may prevent printing, especially if I have hidden text with an opaque rectanglular box, which I have found is ignored if the .pdf is printed. Has any other user experienced this problem and, if so, does any user know of a solution? So far, the only solution I know of is to export it as an unsecured .pdf and then upload it as such. That means overwriting the original "SECURED" .pdf with the unsecured .pdf or amending the filename during the upload process.