Changing background colour for *all* pages of a PDF that is opened in Draw

[martinu]

My wife is finding that PDFs that have black writing on a white background are difficult to read on her tablet because the contrast is too great. She would like to change the background colour of some PDFs to light grey or sepia.

Draw can open a PDF, and there is the Properties option which has Page | Background | Colour (and also Margin: None). However this seems to change only one page, even if you Shift-Click to select a range of pages in the Pages list on the LHS of Draw. So it is necessary to go through each page and make the same change.

What is the way to achieve a global change of page background colour. priot to saving the modified PDF?

[Zizi64]

Can you upload a .pdf or .odg sample file here?

[EarnestAl]

Here is a way to open a pdf in Writer and alter the page style:

1. Click File > Open
2. Click the Open dialogue field where it says “All files (.)” and in the second list starting with .odt, scroll down to the bottom of that list till just before the the dotted line you will find PDF - Portable Document Format (Writer) (.pdf), select it.
   
   
3. Choose the pdf that you want to open and click Open
4. In the Styles pane, choose Pages Styles.
5. Right click master-page3 and select Edit style
   
   
6. In the Area tab, select Colour and chose your desired background colour. OK
7. If not all the pages change background colour then right click that page and select Edit style
8. Export as pdf

[martinu]

EarnestAl

That works perfectly! Many thanks.

Interesting that if I simply did File | Open in Writer, and highlighted the PDF, it opened it in Draw because my PC has a file-association between PDF and Draw. It’s necessary to specify the file type explicitly (as your instructions say). Weird.

[EarnestAl]

Note that Adobe Reader in Windows will allow you to view the document with a background colour and by not altering the document. This is better because you aren’t altering the document, it uses embedded fonts and it applies to all documents that you open. Other pdf reader might offer similar options

1. Open Adobe Reader and click Edit > Preferences
2. Click Accessibility. In the pane click the box Replace Document Colours then choose a Page Background. OK

[Edit]
For Android you can set the tablet to Dark Mode, start Adobe Acrobat and open the file, then click the hamburger at the top and in View Settings turn on Night Mode to get black background with white text instead.

[Wanderer]

@martinu

Interesting that if I simply did File | Open in Writer, and highlighted the PDF, it opened it in Draw because my PC has a file-association between PDF and Draw. It’s necessary to specify the file type explicitly (as your instructions say).

This is not about file-type associations, but an internal feature of LibreOffice to choose the “right” module for opening.
.
To work around this, it is necessary to load the desired module first. Then you can also choose the import-filter for this module.

[martinu]

Is the “open in ‘right’ module” behaviour something that can be turned on and off? It would be nice if when you opened Writer and then did File | Open, the file (even if it is a PDF) actually opened in that program.

There is the added problem that if you open a PDF, and then open another one and start typing “PDF” when the File Type dropdown is open (to find it quickly in the very long list of file types), it finds another entry for PDF (Impress) or PDF (Draw).

It seems counter-intuitive that if you explicitly open one LibreOffcie app and use its File | Open menu, you might sometimes find that the chosen PDF actually opens in another app. Is there a way of saying “only show me file types that are opening with the current LO app, and don’t offer any which would open a different LO app”?

“Choose the right module” is probably a useful feature in some cases, but it’s the classic case of being so helpful that it’s actually a hinderance

[EarnestAl]

@martinu I think you are going down the wrong track, LibreOffice is not a pdf reader, nor a pdf editor. Draw has an import filter to read the graphical objects of which a pdf is composed, that is, Text boxes and images and to read their layout positions.
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It falls down in that it cannot, as yet, use the embedded fonts in the pdf. This shows in your sample on my computer where the substitute font needs more room than is available, leading to text overflowing the page and also going over the top of the next text box on the same line.
.
Draw has better tools to see and work around some of these issues but a dedicated pdf reader is better. A quick search reveals that many pdf readers for Android are able to render a background colour for ease of reading. I don’t know what make your wife’s tablet is, but I am sure a similar functionality exists for Apple devices also.