I’m having exactly the same issue. Sometimes(!) Italic texts do not appear in the PDF (Export to PDF function). This occurs in LibreOffice Calc 25.2.4.3, running on Windows 10 Pro. Font used: Arial.
I just took several hours to figure out why and when this happens, this post is the result of that, so I hope that someone can find and fix this nasty bug.
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Steps to reproduce, although its hard to reproduce, it seems very time sensitive and I’ve made the reproducible case as small as I could.
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Here is how I get this problem reproduced within 5 to 10 times of trying all of these steps:
- Store the attachments on a UNC path (
\\server\path\somewhere\...
)
- Close any LibreOffice app
- Wait for 10 seconds
- Open test5.ods
- Wait for 10 seconds
- Accept the message to read of data from the external file (linkeddata.ods)
- Wait for 10 seconds
- Use the Export to PDF button in the menu bar*
- Inspect the exported PDF. (It shows as either
test5-expected-result.pdf
or test5-no-italic.pdf
- the problem is visible in test5-no-italic.pdf
)
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(*) Make sure that in the “File->Export to PDF…” menu, these options these are set:
I think “Gelabelde PDF” (Tagged PDF) is the important one, that must be enabled.
Sorry its in Dutch. 
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What happens
The output sometimes has no italic text in it, like the example file test5-no-italic.pdf
. Whats interesting is if I copy-paste the entire PDF contents to a plain text editor (like notepad++), I do see that the italic texts are present in there.
In some cases (not this specific test case) the italic texts are exported to the PDF, but doesn’t show Italic.
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What should happen
How the test5-expected-result.pdf
looks is what should happen.
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Screenshots
I got this message from the forum:
Sorry, new users can only put one embedded media item in a post.
REALLY? I just took hours for researching this and then I get rejected like this…!?
I’ll try to post them in the next comment.
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Production
In my production I have somewhat larger files that fail like test5-no-italic.pdf
almost 100% of the time after opening Calc.
When I un-italic these texts (so normal text) its working fine.
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Here are the attachments
linkeddata.ods (13.2 KB)
test5.ods (19.2 KB)
I got this message from the forum while trying to post 2 more attachments:
Sorry, new users can only put 2 links in a post.
REALLY? I just took hours for researching this and then I get rejected like this…!?
I’ll try to post them in the next comment.