The general problem is that Acrobat opens PDF files with write access so that PDF files cannot be modified externally by LyX/LaTeX.
The old pdfview used the programs pdfopen and pdfclose to open and close PDF files in Acrobat and it additionally closed and opened the PDF whenever it was changed (to simulate LyX's update button).
Since Acrobat DC (aka Acrobat 15) it is no longer possible to close PDF files in Acrobat. Due to changes in the Acrobat API also the pdfopen program can no longer be used.
Besides this the approach of updating the PDF whenever it changed was always a hack that often killed Acrobat. The reason is that one cannot immediately update the PDF view if the PDF is changed because depending on the size LaTeX needs up to several seconds to generate the PDF. If the PDF is opened while TeX is still creating is one get error messages from Acrobat Acrobat must be restarted - very annoying. During the years I experimented with a wait time to minimize these problems but of course it can never be solved.
The new pdfview version uses a completely different approach:
- it checks if the PDF is opened by Acrobat by reading the window name. If it is found this program windows will be closed. So Acrobat is not ended and other opened PDF files stay opened.
- to update the PDF view from within LyX one has to press the view button, not the update button. Only this way we know that TeX is ready and the PDF can be opened by Acrobat with write permissions.
- the installer now re-synchronize MiKTeX's package database before installing or updating LaTeX-packages. This assures that new packages and renamed packages can automatically be installed when they are missing (fixes bug #9370)
- update the list of LaTeX packages that have to be installed when LyX is installed via the bundle installer for the first time on a PC
- add support for Turkish spell-checking
As discussed with Vincent I added 3 new features:
* LyX can now also be installed over an existing installation of the same LyX version if the users really wants this.
(A message box appears recommending not to do so for test releases and when there are problems with an existing installation of the same release.)
* LyX can now also be installed if the uninstaller executable of a former LyX was accidentally deleted.
(That this case was not handled was more a bug. Thanks Vicent for the pointer.)
* If a user set MiKTeX's automatic package installation to "No" the installer will.
(As discussed with Vincent, if a user has disabled this MiKTeX feature he most probably know the consequences. So respect his decision.)
respect that and not re-enable it.
I would be happy if anybody can spend a translation of the changed installer message.
- known problem: if LyX 2.0.x is installed and you install 2.1rc1, the .lyx file associations will not be updated but if LyX 2.1 is installed on a new PC the file associations work (work is in progress)
- it turned out that the hack to install a stripped-down Perl directly to MiKTEX is not only error-prone, requires admin permission but that it is also not safe because MiKTeX changes the folder structure from time to time. With the new solution Perl is installed directly for LyX like we do for ImageMagick, Python etc.
- for pdfcrop support there is a bug in pdfcriop that the requirement is hardcoded to Ghostscript 32bit - I contacted the pdfcrop author to fix this
