more formating fixes, additional information

doc/README.Converters.md

@@ -1,20 +1,37 @@
 # Commands for converting documents
 
-This file contains commands for converting different document types
-into
+SeedDMS has a very sophisticated file conversion process which could
+be used to convert any format into any other format, if there is either
+a command (on the command line) or a SeedDMS extension with php code
+doing the conversion. This could of course use an external service
+(e.g. Tika) for doing the conversion. There are already several
+extensions for this purpose and SeedDMS provides some buildin
+conversions as well. Traditionally, conversion was just used
+internally by SeedDMS (and this is still the main purpose), but
+this may not be the only use case.
+
+This file only contains commands for converting different document
+types into
 
 * text (for fulltext search)
 * png (for preview images)
 * pdf (for pdf documents)
 
-Such conversions may not necessarily output an excact equivalent of
+Most of the required commands can easily be installed on a Linux
+server, which is the preferred plattform anyway. Other operating
+systems may work as well, but your milage may vary.
+
+The conversion commands can be configured in the settings of SeedDMS.
+
+A conversion may not necessarily output an excact equivalent of
 the input file, but outputs a suitable representation, e.g.
 converting an mp3 file into text may output the metadata or even the
 lyrics of the song. Converting it into a preview image may result
-in a picture of the album cover.
+in a picture of the album cover, or a graphical representation
+of the spectrum.
 
 Please note, that whenever a command outputs anything to stderr,
-this will considered as a failure of the command. Most command line
+this will be considered as a failure of the command. Most command line
 programs have a parameter (.e.g. `-q`) to suppress such an output.
 
 If you run php-fpm you may encounter problems with charsets based on
@@ -25,19 +42,26 @@ UTF-8 chars. In such a case you may want to set `clear_env=no` in
 php-fpm's configuration. On Debian this is done in the file
 `/etc/php/<php version>/fpm/pool.d/www.conf`. Search for `clear_env`.
 
+The following sections will list possible conversion commands for
+extracting text, creating an image, and converting to pdf.
+
 ## Conversion to text for fulltext search
 
 ### text/plain, text/csv, application/csv
  
 `cat '%s'`
 
+Unless you run a very old version of SeedDMS, you will never need
+this command for converting text files. SeedDMS has this trivial
+converter build in.
+
 ### application/pdf
 
 `pdftotext -q -nopgbrk %s - | sed -e 's/ [a-zA-Z0-9.]\{1\} / /g' -e 's/[0-9.]//g'`
 
-If pdftotext takes too long on large document you may want to pass parameter
-`-l` to specify the last page to be converted. `-q` is for suppressing error/warnings
-send to stderr
+If pdftotext takes too long on large document, then you may want to
+pass parameter `-l` to specify the last page to be converted. `-q` is
+for suppressing error/warnings send to stderr
 
 `mutool draw -F txt -q -N -o - %s`
 
@@ -65,6 +89,8 @@ send to stderr
 
 `html2text %s`
 
+### Many office formats
+
 Many office formats can be converted with `unoconv`, though this turned
 out in the past to sometimes crash or taking a long time.
 
@@ -79,6 +105,13 @@ plain text in return.
 Of course this requires to first install Apache Tika when using the docker
 image.
 
+Finally, there is a SeedDMS extension
+(unoserver)[https://codeberg.org/SeedDMS/unoserver] which is based
+on a project also called
+(unoserver)[https://github.com/unoconv/unoserver] and which is
+available as docker image, making it quite easy to setup. Read the
+documentation of the extension for more information.
+
 ## Conversion to pdf for pdf preview
 
 ### text/plain, text/csv, application/csv, application/vnd.oasis.opendocument.text application/msword, application/vnd.wordperfect, text/rtf
@@ -89,7 +122,10 @@ image.
  
 `convert -density 300 '%f' 'pdf:%o'`
 
-Actually `convert` can be used for many other image formats.
+Actually `convert` can be used for many other image formats. There is
+also a SeedDMS extension called
+[convert_image](https://codeberg.org/SeedDMS/convert_image) which
+embedds the image into a pdf file.
 	
 ### image/svg+xml
 
@@ -125,15 +161,23 @@ Converting from application/x-xopp to pdf only works if the xopp file
 does not use a pdf document as a background, because this pdf is not
 stored in the xopp fіle.
 
+### Many office formats
+
+As already mentioned above, `unoconv` has some disadvantages. It is
+recommended to the `unoserver` SeedDMS extension already described
+above.
+
 ## Conversion to png for preview images
 
 If you have problems running convert on PDF documents then read the page
 https://askubuntu.com/questions/1081895/trouble-with-batch-conversion-of-png-to-pdf-using-convert
 It basically instructs you to comment out the line
 
+```
 <policy domain="coder" rights="none" pattern="PDF" />
+```
 
-in /etc/ImageMagick-6/policy.xml
+in `/etc/ImageMagick-6/policy.xml`
 
 `convert` determines the format of the converted image from the extension of
 the output filename. SeedDMS usually sets a propper extension when running
@@ -182,6 +226,10 @@ why the input needs to be recoded with iconv or recode.
 
 `unoconv -d document -e PageRange=1 -f pdf --stdout -v '%f' | gs -dBATCH -dNOPAUSE -sDEVICE=pngalpha -dPDFFitPage -r72x72 -sOutputFile=- -dFirstPage=1 -dLastPage=1 -q - | convert -resize %wx png:- 'png:%o'`
 
+If you are looking for an easier solution, you should consider to
+install the `unoserver` SeedDMS extension which was already described
+above.
+
 ### video/webm, video/mp4
 
 This will take 12th frame of a video and converts into a png. It requires