Thanks for your reply and for your advice about reproducible example.
I checked that Preview isn't the default app for Word documents in the Finder.
I also ran this simple .Rmd example, and the results is the same.
---
title: "test"
output: word_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
## R Markdown
This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.
When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
```{r cars}
summary(cars)
```
## Including Plots
You can also embed plots, for example:
```{r pressure, echo=FALSE}
plot(pressure)
```
Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.
Any suggestion?
Thanks in advance
> sessionInfo()
R version 3.6.0 (2019-04-26)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS 10.15.1
Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib
locale:
[1] es_ES.UTF-8/es_ES.UTF-8/es_ES.UTF-8/C/es_ES.UTF-8/es_ES.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] reprex_0.3.0
loaded via a namespace (and not attached):
[1] Rcpp_1.0.3 ps_1.3.0 digest_0.6.23 R6_2.4.1 evaluate_0.14
[6] rlang_0.4.2 fs_1.3.1 callr_3.3.2 whisker_0.4 rmarkdown_1.17
[11] tools_3.6.0 xfun_0.11 yaml_2.2.0 compiler_3.6.0 processx_3.4.1
[16] clipr_0.7.0 htmltools_0.4.0 knitr_1.26